April 6, 1888.] 



SCIENTIFIC NEWS. 



325 



be recognisable. They bark mostly by night, like all 

 frogs, and when heard by day, it is usually in this half 

 croaking manner." 



English Trout Eggs for India. — The Fis/iiiig Gasette 

 states that Mr. W. T. Silk, of Burleigh-park Fishery, 

 Stamford, recently shipped to India for Major Hodgson 

 10,000 English trout eggs, and hopes from these eggs to 

 stock some streams in the Neilgherry hills, in the South 

 of India. 



A Great Auk's Egg. — On the 12th March, Mr. Stevens, 

 of King Street, Covent Garden, sold a very fine egg of 

 the great auk for ;£22S. It had been in the possession 

 of the late owner since 1851, when it was purchased for 

 _;^r8. This is the highest price ever paid for an egg, 

 and is an advance of _;^57 on the sum paid for a great 

 auk's egg of which we recorded the sale last December. 

 We gave a description of this bird on page 59 of this 

 volume. 



Weight and Dimensions of a Tiger. — Mr. F. A. 

 Shillingford gives, in the Calcutta Englishman, the follow- 

 ing particulars concerning a tiger recently killed at 

 Purneah : Weight, 52oi lbs. ; length from tip of nose to 

 root of tail, 6 feet 5 inches ; height at shoulder, 3 feet 

 9 inches. This record is of some value, as sportsmen 

 generally include the tail in the measurement of the 

 animal ; and as the length of this member bears no 

 fixed proportion to the size of the tiger, the figures are 

 useless. 



Abnormal Colouration in a Cat. — Some years ago 

 the generahsation was suggested that, if any black colour 

 was found at all in feline animals, it would certainly 

 occur at the tips of the tail. In dogs, on the contrary, 

 the tip of the tail was alleged to be always white, if that 

 colour occurred in the animal's coat at all. Last summer 

 I happened to see in Hatton Garden a singular exception 

 to the former rule in the shape of a glossy black tom, 

 with the tip of his tail a pure white for about two 

 inches. — J. W. S. 



Variation in the Edelweiss. — According to the In- 

 dependent Statesman, of Concord, the edelweiss, when 

 transplanted from the Alps to the mountains of Upper 

 Austria, bears red flowers instead of blossoms of its 

 ordinary greyish-white. This, however, we cannot, like 

 our contemporary, regard as " transformation into a new 

 species," to which very much more would belong than a 

 change in the colour of the flowers. Has the edelweiss of 

 New Zealand a different colour from that of Switzerland ? 



The "Dicky-Bird Society." — We are glad to learn 

 from Mr. H. Kerr {Newcastle Weekly Chronicle) that this 

 strangely-named society is meeting with great success. 

 No fewer than 148,000 children have pledged themselves 

 to refrain from and discourage bird-nesting, bird- 

 catching, etc. Meantime the Selborne Society, now 

 1,160 strong, is combatting the evil practice of using 

 birds or parts of birds for m.illinery and dressmaking 

 purposes, and in America the Audubon Society is work- 

 ing on the same lines. We hope that public opinion 

 will soon be sufficiently enlightened to allow of the 

 Legislative prohibition of the importation of humming- 

 birds, trogons, birds of paradise, etc., for such shameful 

 purposes. 



MODERN PHOTOGRAPHIC ENGRAVING 

 AND PRINTING.— I. 



A Paper by Mr. George S. Waterlow, read at the 



Conference of the Camera Club. 

 The subject of the modern application of photography 

 to the art of engraving and printing is one of stupendous 

 interest to all communities, of immense value to future 

 generations, and teems with interesting details. I can- 

 not but feel that within the compass of this short paper 

 which I have the honour to place before you this evening, 

 it is not possible or desirable that I should attempt any 

 historical account of the various researches and experi- 

 ments which at the present time place us in possession 

 of the means of illustrating by practical and easy 

 methods every subject of art, life, and nature, methods 

 but vaguely dreamed of a generation ago, even by the 

 most sanguine enthusiasts. 



Neither should I endeavour to criticise the merits of 

 specific processes or the busy researches themselves, but 

 I am here simply to describe to you as concisely as pos- 

 sible some of the means by which to-day we may pro- 

 duce illustrations of every description through the 

 powerful agency of the camera. 



First, I will take the names of some of the various 

 methods, and then describe the practical working of 

 each as plainly as I can, avoiding the use of technical 

 terms. 



Modern photographic engraving and printing may be 

 divided into four heads : — 



I Typographic blocks, which are etched in relief, 

 and printed from the surface in an ordinary printing- 

 press. 



2. Plates, which are etched in intaglio, and printed 

 from the depth, as in the case of an engraved copper 

 plate. 



3. Woodbury blocks, which are impressed with an in- 

 taglio image by a gelatine relief under great pressure, 

 and printed from by a special press. 



4. Collotype or Albertypc plates, i e., a surface of gela- 

 tine on glass or metal, which has been sensitised, acted 

 upon by light through a negative, and is printed from in 

 a hand or steam-printing press. 



The most important of the many photographic methods 

 now before the world for mechanically producing prints 

 on paper in the printing-press is that which is popularly 

 named photo-zincography, and is the first referred to on 

 my list. 



Before proceeding to a description of the working of 

 this useful process, I might explain, for the benefit of the 

 tyro, that nearly all the results obtained by these pro- 

 cesses are founded on the simple fact that gelatine, in the 

 presence of salts of chromium, is rendered insoluble in 

 exact proportion to the amount of light allowed to fall 

 upon its surface. In this peculiar property of the organic 

 substances previously soluble in water, as in the case of 

 gelatine, lies the whole secret of nearly every photo- 

 mechanical process, and in its various modifications lie 

 the initiatory stages of all the dificrent categories just 

 mentioned to you. 



I will briefly explain this action. Suppose I dissolve 

 ten grains of gelatine in an ounce of water, and add ten 

 grains of bichromate of potash (K,Cr,Oj), then coat a 

 sheet of smooth writing-paper with the mixture and dry 

 it in the dark. On now exposing this piece of prepared 

 paper under a negative of a drawing in lines for, say, ten 

 minutes in sunlight, I obtain a faint image or print of 



