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the three negatives, in other words, would have all the appearance of having been correctly exposed.

Why trouble about speed numbers?

The reader may well ask, if this is so, why trouble about speed numbers at all? Before answering the question, let us take another imaginary case.

we

We will suppose there are three more plates in the camera, of the three speeds just mentioned, and that have to snapshot some object which is moving, and that consequently we know that we must not give a longer exposure than 1-100th second, or it will be blurred; yet the correct exposure with the fastest plate is 1-30th, and with the slowest 1-20th second. If we give 1-100th second, we are giving one of the plates less than one-third the exposure it should have, one is only having one-fourth, and the slowest of all one-fifth of the correct time. We give all three 1-100th second, however, and develop them, as before, side by side in the same dish.

On comparing the finished negatives in this case, we are much more likely to find a difference. Judging it by the eye, putting it down on a sheet of white paper for the purpose, the fastest plate of all may seem the least underexposed, as might have been expected. Even here we might be misled. Suppose we made as good a print as we could from each, using the same sort of paper for all three, and showed these prints to some experienced photographer, asking him for his opinion as to the exposure, it is quite possible that he would pronounce the print from the slowest plate as the best exposed, and vice versa.

If we made a third series of experiments, giving all three plates the same exposure again, but this time taking care that that exposure was, say, twenty times what we found to be the correct one, we might get a similarly confusing set of results.

One conclusion that could be drawn from these experiments, which have often been made, is that the question, What is the speed of a plate? is not quite so simple as it seems. Two plates which, when under-exposed, indicate that A is faster than B, when over-exposed may indicate that B is faster than A; when correctly exposed, A and B may appear of the same speed. A second conclusion, and for my present purpose it is a very important one, is that, although if we have two lots of plates, one marked "H. & D. 100 " and the other "H. & D. 400," the latter may be taken as being four times as fast as the former, differences as small as those between H. & D. 200," "H. & D. 250," and 'H. & D. 300," when they exist at all, are not distinct enough for the novice to take into consideration.

Ultra-refinements.

In the previous paragraph I underlined the words "when they exist at all" because when we buy two boxes of plates of different makes, both bearing the same H. & D. number, it does not follow that they are of the same speed; or if one is marked "H. & D. 200" and the other "H. & D. 300," that one is faster than the other. If they are of the same make, we shall be correct in such a supposition; but if they are of different manufacture, the 'H. & D." numbers may not have been worked out in the same way, and so may not be comparable. There are differences of opinion as to the way in which such numbers should be ascertained; different plate-makers use different methods, and the subject is too complex for much hope of a definite agreement. Fortunately for the users, these differences have no practical value. The numbers suggest refinements which are not to be detected in actual work. Moreover, if we select some one brand and stick to it, we can ignore the figures on the box. The

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March 29th, 1922.

plates or films of any of our leading makers are so uniform in rapidity and characteristics that if we buy three boxes at intervals of a year or two, and give the contents of all exactly the same exposure, we shall find that we get identical negatives.

a

Watkins & Wynne numbers.

Hitherto I have written of "H. & D." numbers only. Many boxes bear 'Watkins" number, or a "Wynne " number, or both. An additional testimony to the difficulties of the subject may be found when a box by one maker is marked "H. & D. 250, Watkins 180," and by another maker H. & D. 400, Watkins 180," showing that by one system these plates have the same speed and by another they are of different speeds.

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The makers of the Watkins and of the Wynne exposure meters supply cards giving the speed numbers of the various plates and films according to the particular system which those meters employ. Anyone using such a meter, and I strongly recommend every beginner to do so, will get such a speed card with it, and can work by it, ig noring altogether the marks on the boxes.

Before leaving this subject I ought to add a word or two to prevent misunderstanding. It is to the interest of every plate-maker that his material should be properly treated; and the figures given on the boxes may therefore be accepted in all good faith. It is not suggested for one moment that plates are deliberately wrongly marked, or indeed that they are wrongly marked at all. So long as the confusion between different methods exists, and so long as there is even no general agree ment on a definition of rapidity, there are bound to be such differences if numbers are given at all. In my own opinion it would be best to omit them; but that I recognise is a counsel of perfection. R.C.B.

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& PHOTOGRAPHY

March 29th, 1922.

T

nor

HERE being no date to it I have no idea how long I have had a letter now before me. It has often been pointed out that a nice easy way of dealing with correspondence is to keep the letters for so long that a reply would not serve any purpose. The writer's address would not be known for certain, for one thing. What was The Towers then might be the County Gaol now. It is of no use anyone expecting an early replyas everyone seems to do-if he sends neither name address. Even if I wrote a reply at once, which is wildly improbable, some weeks would elapse before it appeared in print. A name and address do not materially increase the chances either, unless payment is made in advance towards the cost of the secretary who takes down and types the reply and of the footman who conveys it to the post. I do quite enough in the way of correspondence as it is, and take credit for being personally responsible for the greater part of the Post Office surplus of eight millions, over which there is so much squabbling.

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The somewhat ancient letter to which I refer asks me to advise the writer whether or not he should purchase a large quantity of carbon bisulphide which has been offered to him at half-price. If it is still available-and the smell may be taken as sound and sufficient evidence-I hope this reply will be in time. He should certainly buy it, even at double or treble the cost price, whatever it may have been. There are few more desirable things to have handy than a large stock of carbon disulphide (as I prefer to call it), provided the fire insurance is adequate, and the premium paid and acknowledged. The would-be seller has stated that he added some to a hypo solution, and that a print placed in it for half an hour expressed its appreciation in the warmest terms. This is highly probable; but it is not for photography that I recommend carbon disulphide as a desirable acquisition.

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After all, photography is not everything. The CS, is a most economical substitute for expensive perfumes. A little of it goes a long way. In fact, that is one of its few drawbacks. Many will think it goes much too far, and that the very rottenest egg cannot pretend to be in the running with it. A pint or so poured hurriedly over a dull fire works wonders, and it is also useful for applying to tobacco pouches and other articles of unvulcanised rubber. But it is as an adjunct to the bathroom that it really distinguishes itself. A gallon of CS, to each pint of bath (or one metre to the cubic milligram) has an effect that only experience can teach one to appreciate. The person who enters the bath slowly and reluctantly comes out with a vigour that is positively amazing. It is a rejuvenator and accelerator of unparalleled potency. So I certainly advise my correspondent to buy all he can get, and use it in as many ways as he can think of. As a beverage it lasts longer than alcohol, and its use as a salad dressing never passes unnoticed.

I hope, however, that these encomiums on a chemical that has not hitherto received the appreciation it deserves will not inspire readers to invest over-rashly in carbon disulphide. They should bear in mind that the time of the annual Photographic Fair at the Haughty Cultural Hall draws near, and that it is preceded by quarter-day. It is no time for wholesale transactions in CS,, and a couple of barrels should be considered the limit in ordinary cases. Only a week or two and readers will be bashing open their tin money boxes to see if they have saved enough farthings to buy a trial box of the new Greased Lightning plates that are to make their début at the Fair.

I venture to prophesy that on this occasion there will be, if possible, fewer free samples than ever at that fête, but I understand that, by way of compensation, the orchestra are soldering a new top note on to their inevitable barcarolle. I believe, too, that there will be a book on sale of so tempting a character that those who have stumped themselves by extravagant purchases of carbon disulphide, or other luxuries, will be falling over each other for pass-out cheques so that they can sprint to the nearest place with a trio of spheres over the portal to raise the wind. I have no further reliable information as to what there will and will not be at the Fair, and do not care much so long as there is an adequate supply of stone ginger in the usual corner. Of course, there will be a contemporary strike of some kind or other. There always is. But it will have to be something extra special to have any effect on the proceedings.

Any reader who happens to have a clockwork aeroplane ior disposal may be brought into touch, through me, with another reader who wishes to acquire one for purposes of international transport. He offers in exchange his photographic apparatus and the sole rights in several ideas of his own. One of the latter is a method for producing scratches on the film of any glass plate, with a companion method for completely removing them. The apparatus for the first process is already complete, and works well; but he has not yet made any progress with that for the second. He has an original shutter working at slow, slower, half-time, and stop, which seems a great advance upon anything else of the kind, and should alone be well worth the aeroplane. Another valuable item of his outfit is a camera of which the top is removable so as to admit more light to a plate that might otherwise be under-exposed; and it is also fitted with an automatic clutch for joggling the plate about during exposure so as to hank the results well up to exhibition standard. For a really reliable flier he will throw in an exposure calculator, by means of which any exposure can be found by multiplying the distance of the object by its focal depth and subtracting the remainder. Please do not send any aeroplanes along to me. Just write about them and wait till you hear further.

I heartily wish that readers would refrain from asking me to stir up the Editor about one thing or another. The mere thought of it is disquieting. They must do their own stirring up. One such reader, from the safe distance of New Zealand, suggests some of this stirring up, to the end that there may be a competition for colonial readers, with sufficient time given to send the prints in. Why, the very thing has been going on for years. And the conditions are such that we get nothing of the sort here at home. The only conditions are that anyone can send in anything and choose his own prize. That ought to be good enough. It would suit me, although I am not sure whether I should be asked to send in anything first. The prize arrangement is all right, but it is such a beastly nuisance having to do anything for an award in addition, to selecting it. The New Zealand gentleman says that the Editor does not seem to realise that it takes eight weeks each way for things to travel by post, and yet the Editor allows nine months between the printed notice of the competition and the date for receiving the request for a plaque. If this is not enough, I can only suggest that New Zealand photographers charter a cheap tug and haul their funny islands a bit nearer home, and while they are at it they might remember to chuck a tow-line to one or two still more distant islands in the Pacific and Antarctic oceans. THE WALRUS.

& PHOTOGRAPHY ✔ ✔

he was elected on its Council two years later, and became President in 1909. He has also been curator. He is a strong advocate of weekly meetings for photographic societies, holding that this has an important. bearing upon their success. The members can form the habit of setting aside the club night, for which any day in the week may be chosen, and therefore can easily remember the fixture. He also believes that all officials should be elected annually, including the President, who should not be eligible for two years in succession. He holds that a society should neglect no phase of legitimate photographic work, giving the word "legitimate" the widest possible meaning, and recognises that social functions, if not overdone, are a valuable factor in the success of a society. Mr. Linley, who is a B.Sc. of London University, is interested both in the technical and pictorial aspects of photography, and in scientific subjects generally. He uses platinum and bromide chiefly, but appreciates any good medium, and thinks that both carbon and gum-bichromate are quite undeservedly neglected.

April 5th, 1922.

of the light are two actions which go on side by side; and backing, however efficient, can only deal with the halation. The actual staining of the film

by the dye which is intended to act as the light filter checks both. After passing into a film of emulsion that has been stained in this way, the photographic activity of any light which may be scattered in the film, or which may pass through it into the glass to be reflected and so give rise to halation, is very much reduced. While it is not reduced enough to be a complete preventive in the case of a difficult subject, it is lessened so that in mild cases it is inoperative. This is one reason why plates of this kind give such clean, bright images. Halation is often present and acting injuriously on the character of the negative, when it is not actually recognised as such. This was brought home very forcibly to us when testing a number of backing preparations, by painting over one-half of a plate with the backing, and leaving the other half bare. The backed half was often conspicuously better than the unbacked half, although neither, considered by itself, would be said to be halated. The defect was very visible when the glass side of the plate was looked at after development but before fixing, the high lights being surrounded by a very distinct halo of deposit. This was no longer visible when the negative was fixed; but although the image may have masked it, more or less, it must still have been present undoubtedly, tending to make the negative less bright than it should have been.

HAT constitutes a "serious worker"? We are constantly hearing photographers classified as "button pressers and as "serious workers," that one almost comes at least to believe that there is some distinct division between them. Yet on looking into things it is by no means easy to discern any such division, or to draw such a line that, by general acceptance, "serious workers" will all lie on one side of it, and "button pressers on the other. It cannot be decided by the mere size of the resulting pictures, as we have heard suggested; as every society contains expert members who work with the tiniest of cameras, and not all of them resort to enlarging. Nor would it do to define "button pressers as those who let the chemist do, not only the developing, but also the printing and mounting, for there are people who do the whole of their photography themselves, whom no one would class as serious workers."

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It is always difficult to decide "where to draw the line; and it is only in parliaments, debating societies, and similar word-chopping institutions that it is accepted that if we cannot decide where to draw the line, it is evident that no line can be drawn, and that the persons or things referred to cannot be classified.

We should like everyone who reads this to put the question to himself: "Am I a mere button presser, or am I a serious worker?" And if in modesty he feels that to class himself as a serious worker is to claim a status that he does not deserve, let him remember that the term does not refer to the quality of his work, but simply and solely to the spirit in which he performs

it.

His prints may be of the crudest and most imperfect kind-we all have to begin at the bottom; but if he takes his photography seriously, if he has once grasped the fact that there is something to learn in photography before he can make passable photographs and is trying to learn it; if he thinks that his camera, instead of being a mere toy for a moment, can be a constant and inexhaustible source of interest and occupation; if the mere doing of some photographic operation is in itself a pleasure to him, irrespective of the result-then the class in which he should be placed is clear enough.

Regarded in this light, almost all who read this will have to admit that they are "serious workers." The mere fact that The Amateur Photographer and Photography is read, or even looked at more or less regularly, reveals a serious interest in the hobby-not an interest that must make the reader an exhibitor or an expert authority, although it may do so, but one which will enable him to get far more pleasure out of his camera than he can ever do when he uses it only on a holiday or for a few snapshot portraits.

Every such photographer, however much of a novice now, may fairly regard himself as a "serious worker "; and, doing so, should do all he can to bring others into the ranks. Widespread as our hobby is to-day, we believe that the total occupation and pleasure that is got from it is not one-third what it could be made to yield if every owner of a camera could be led to realise what lay within his reach.

We can all do something to help to bring this about