US 



KNOWLEDGE 



[April 2>^, 1882. 



fow hours, when it will lie found that the creamy appear- 

 ance of the plate, which may have been noticed two or 

 thre.e niinut<\s after it was placed in tlie solution, will have 

 disappeared. This " creamy " appearance is caused by 

 the conversion of the iodide in the collodion into iodide of 

 silver. Unless the silver solution be treated in this way, 

 it is too active, and no certainty could be placed in the 

 plates. Add one drop of nitric acid, and then the bath 

 should be filtered. 



VV^e are now ready to make use of the collodion and 

 silver solution, but all tlu^ operations after the plate is 

 coated with collodion must be conducted in a darkened 

 room. In ord(T to practice photography with pleasure 

 and comfort, it is necessary to have a room specially 

 arranged, or, at least, a portion of a room, the 

 window of which may be darkened without much 

 trouble. White light must be quite excluded, and this 

 may be effected by covering a frame with black calico or 

 brown paper, leaving about two or three feet, which may 

 be covered with yrllow paper. This will admit sufficient 

 light to work Ity, and the light, passing through the yellow 

 paper, being rendered non-actinic, is harmless, and the 

 sensitive collodion film may be manipulated without 

 fear of injury. The frame may be made removable, but 

 it must fit so as to admit no white light. If convenient, 

 a sink should be arranged, and a supply of water laid 

 on. There should be a shelf for bottles and a table for 

 the bath and other things in use. If the room cannot 

 be used exclusively for photographic purposes a cupboard 

 should be appropriated. One thing to be carefully avoided 

 is dust. 



If such information should be required, the dealer who 

 supplies the camera and lens will show how to " focus " an 

 an object. The ambitious amateur will probably think the 

 best subject for his first essay should be a portrait, but our 

 advice is decidedly in favour of a more simple subject. If 

 in a room, place a table near a window with a good north 

 light, and on the table place a statuette or any other 

 suitable object. If it is preferred to work out of doors, it 

 matters very little what the object may be ; an engraving 

 placed in a vertical position, with the camera arranged 

 " sqitare" before it, would be an easy subject. 



We are now ready to prepare a plate. Take one of the 

 cleaned plates, and see that it is free from dust. Specs of 

 du.st would form small black spots in the negative, for we 

 are about to take a ?jP(7rt<;'i'«, ^' //lass positives " being quite 

 out of date. Hold the glass by one corner in the left hand, 

 then pour on to it what may appear to be sufficient col- 

 lodion to cover it. Allow the fluid to flow to each 

 corner, carefully preventing it touching the thumb 

 holding the plate, otherwise, the surplus collodion may 

 run where it is not required ; then pour off into the 

 bottle, move the plate " to and fro " for a second or two to 

 prevent the collodion " SPtting " in streaks. The collodion 

 bottle can now be put aside, and the stopper replaced. 

 One corner of the plate may be touched, and it will be 

 seen whether the collodion has set. Put the plate 

 at once on to the dipper, and slowly lower it into 

 the bath, but do not hesitate. A halt for a moment 

 would cause a line to be marked on the plate which 

 would spoil the negative. The bath should be in 

 such a position with respect to the light that the plate can 

 be easily inspected. After about three minutes, it may 

 be withdrawn from the solution, and if it look " streaky " 

 it is not yet ready, and it must remain in the bath of 

 nitrate of silver until it presents an even surface when 

 withdrawn. When ready, the plate must be placed in tlie 

 "dark slide" of the camera with the prepared surface down- 

 wards, that is, facing the lens when placed in the camera. 



Up to this point, everything should be done deliberately 

 and without hurry. In hot weather it is desirable that 

 the time between taking the plate from the bath and its 

 development should not be longer than neces.sary, in order 

 to avoid the drying of the plate or the partial drying. All 

 sorts of troubles arise if too much of the silver solution Ls 

 allowed to drain away, but we must not linger here to 

 describe what those troubles are. Probably by the time 

 they are first seen the amateur will have become sufScientlr 

 expert to detect the causes of his failures. 



No rule can be given as to the proper time necessary to 

 " expose " the plate, as much depends on the state of tile 

 light ; one or two trials should be made. If the picture 

 " flashes " up too quickly, too much time may have been 

 given ; and if the image does not appear in a few seconds 

 after the developing solution has been poured on the plate, 

 two little time may have been given — experience alone is 

 required. In a good negative there should be a proper 

 balance in the lights and shades. A very little practice will 

 suffice to determine this point. 



The next important operation will be the development 

 of the pictures, and this must be deferred till the next 

 paper. Up to this point the amateur can be getting into. 

 working order. 



CHARLES R. DARWIN.* 



By THE Editor. 



CHARLES DARWIN, the Newton of Biology, died 

 on Wednesday, April 19, 1882, aged 73 years. He 

 was born on Feb. 12, 1809, at Shrewsbury. His father 

 was Dr. R. W. Darwin, F.R.S. ; his grandfather Dr. 

 Erasmus Darwin, F.R.S., author of "The Botsoiic 

 Garden," " Zoonomia," and other works. Shrewsbury 

 Grammar School may fairly be proud of the circumstance 

 that the most eminent naturalist of the nineteenth century 

 was trained under her care. In 182-5 Darwin left Shrews- 

 buiy for Edinburgh, where he attended the University 

 lectures for a period of two years, at the end of 

 which he entered at Christ College, Cambridge. He 

 took his degree in 1831. In this year he learned 

 that Captain Fitzroy had offered to share his cabin 

 with any competent naturalist who would accompany 

 him in H.M.S. Beagle, which was about to sail on 

 a voyage of circumnavigation. Darwin tendered his 

 services, and doubtless the world owes to this circum- 

 stance, more than to any other, the wideness of Darwin's 

 views as a naturalist, and the noble generalisation with 

 which his name will in all future time be associated. 

 The voyage in the Beagle has been described by himself 

 in one of the most delightful works in the English 

 language. The charm of foreign travel to a mind imbued 

 as Darwin's was with a sense of the significance of all 

 Nature's teachings, is gi-aphically presented in the " Jour- 

 nal of Researches into the Geology and Natural History 

 of the Various Countries visited during the Voyage of 

 H.M.S. Beagle Round the World." 



Returning home with shattered health, but with his 

 mind prepared to search successfully into the secrets of 

 Nature, Darwin was in no haste to propound crude or 

 immature speculations. The facts he had observed, seemed, 

 he tells us, to " throw some light on the origin of species — 

 that mystery of mysteries, as it has been called by one of 

 our greatest philosophers." But fanciful imaginings were 

 not the means by which this light was to be concentrated. 



* Abridged from a biographical notice (by the Editor of Kxow- 

 leuok) whicli appeared in the Daily Nev:s for Friday last. 



