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July 20, 1883. | THE PHOTOGRAPHIC NEWS. 455 Headings. Mark. E Headings. Mark. F Gas F The former, you observe, behaves in a similar manner latter as regards sensitiveness, and contains per fluid Mark. G another lot done with N+water Eotes H 4 ... 26 ... 25 8 ... N- 6 5 ... ... 27 ... 26 3 4 5 6 30 30 32 64 14 9 12 23 24 25 20 1 2 3 4 W W s s W w s s 5 6 7 8 14 9 13 22 N+AmHO N+AmBr 2. 15 12 11 23 18 20 22 23 25 19 15 12 14 23 We are glad to hear that no less than 8,000 francs have been subscribed towards the Poitevin memorial. Developer employed. Normal 30 80 30 64 f N-=vol of pyro. I solution ... : Pyro. sol.=2 gr. per oz. 30 30 30 30 (8 times) W S S s Series F exhibits the relative action of the alkaline pyrogallic and ferrous-oxalate developers respectively:— 14 9 12 21 as shown in Series E. The advantage of this arrangement above all others is—firstly, there is no medium between the source of light and the film ; secondly, there is no appreciable deteriora tion by use ; and thirdly, they can be produced in any quantity, as every part is based entirely upon measurement, and conse quently may be regarded as a mechanical standard equal with a Whitworth gauge. With regard to the accuracy with which the holes can be made, it is only necessary to have gauges similar to these, which are made the size of every hole ; these can easily be measured by means of a micrometer, or the holes by means of slightly conical rods. Series E shows the comparison between Mr. Warnerke’s instrument and my own, with two phosphor- the other, film to film ; it is then a matter of comparative ease to bring any oue of the tinted triangles opposite to any other particular one, for the purpose of judging their respective in tensity with the idea of determining the gradation of range of tint produced. I have to thank you for your very kind attention, and trust that this contribution may assist somewhat to elucidate the best means of obtaining a standard of comparison for prepared sensi tive films. so as to hold the sheet to be exposed, and keep it smooth against the plate of glass, d; when the sheet has been exposed, the board is drawn back from the glass in order to release the exposed sheet, and allow it to be rolled on the exposed roller: the board is kept back while this is being done by turning the square rod c2 half round, so that the angles of the square will not pass back through the square opening until again turned opposite to it; e e are doors, by opening which the operator can see (through the yellow glass y y) to adjust the position of the sensitive sheets when changing them. 3 minims of ammonium-hydrate. sp. gr. 0'880, 2 grains of ammonium bromide, and 1 grain of pyrogallic acid, and is adopted by Mr. Swan for developing his plates. Having arrived at a method of determining the sensitiveness or time necessary to register the minimum tint upon a film, we will next apply the instrument to the study of the difference in the relationship that is found to exist between the tints themselves and the intensities Developer employed. Normal MELHUISH’S ROLLER SLIDE* The object of the slide is to enable a person to carry out any number of sheets of sensitive paper and change them con veniently in the open light. The slide is fitted up with two rollers, a a, and the sensitive sheets, b b, are gummed together, making one long band, the ends of which are gummed to pieces of paper- always kept on the rollers. The sensitive sheets are wound off the left or reserve roller on to the rig ht or exposed roller, until all are exposed. The rollers are supported on springs a 1 al, to render their motion equal; they are turned by the milled heads m m, and clamped when each fresh sheet is brought into position by the nuts a 2 a 2 ; c is a board which is pressed forward by springs, c' c', ... w ... ... s ... ... s ... i ... s ... Ferrous Oxala e. W ••• VI coo ... s ... ... S ... I ... s ... .. 14 .. 9 .. 13 ... 22 to the ounce w w 8 S Gas Mark. fl 2 3 Exposure. 11 . 20 . 40 . 60 . 60 . 60 . Series H similar, except that they were of plates. Time, acting, in minutes. ... 6 .. ... 6 .. ... 6 . Exposure. .. 1 . ,.. 8 . ... 8 . Heading. 1. 2. 19 ... 18 27 ... 26 26 ... 25 Exposure in seconds. Tablet used. Instrument. Time acting in minutes. 8, . 3i 34 3i 4 4 Reading 1. 2. 19 . 21 . 23 . Light Instru- Exposure used. ment. in seconds. Alkaline Pyrogallic. that were used to produce them, partly arising from the character of the films and the developer employed. Series G are produced by modifications of the pyro developer, all of the plates belonging to the same dozen. escent tablets, one being his standard, the other one prepared by myself. I regret that time will only permit my taking more than a passing notice of them. You will observe the range of tint is in some of them increased, whilst in others the opposite effect has been produced. This subject I hope to discuss more fully, with your permission, at some future time, as I find the instru ment to be well adapted for such investigations. The form of stencil mat already described now comes to our aid, for it is only necessary, when you wish to compare one result with another, to reverse one of the plates end for end, and to superpose one upon Mr. C. Ray Woods returns to England by the 8.8. Nile, which is due from the West Indies on the 28th inst. We sincerely trust he will be amply recompensed for his arduous voyage of six months, undertaken to observe a six minutes’ eclipse. * From the Journal of the Photographic Society, April, 1856.