EECREATIYE SCIENCE. 



233 



to the best means for rendering them lasting. 

 This has been found to be more particularly 

 the case with photographs on paper, a want 

 of visibility and a yellow tint in time spread- 

 ing over the pictures. This matter is consi- 

 dered to be of so much importance, that the 

 Council of the Photographic Society ap- 

 pointed a oommittee to inquire into the cause 

 of failure, and to discover the best remedy. 

 Light and moisture are looked on as among 

 the causes contributive to failure; but the 

 committee, after a long investigation, report 

 that the most common cause of fading had 

 been the presence of hyposulphite of soda, 

 left on the paper from imperfect washing after 

 fixing. The action of sulphuretted hydrogen 

 gas in the London atmosphere is another 

 cause ; and they find that there is no known 

 method of producing pictures which will re- 

 main unaltered under the continued action of 

 moisture and atmosphere in London. The 

 committee recommend that trials be made of 

 substances likely to protect the prints from 

 air and moisture, such as caoutchouc, gutta- 

 percha, wax, and the various varnishes. 



Experiments ox Colour by Hekschel, 

 HtrNT,BiOT,ANDBECQUEREL. — SirJohuHer- 

 Schel s tates that, in 18 40, he got some specimens 

 of paper long kept, which gave a representa- 

 tion of the spectrum in its natural colours, 

 giving light on a dark ground ; but he was 

 not prepared to say that they would prove an 

 available process for coloured photographs. 



though it brought the hope nearer. Mr. 

 Hunt informs us that he has obtained coloured 

 pictures of the prismatic spectrum dark upon 

 a light ground, and also on Daguerreotype 

 tablets when iodized. In 1854, he obtained, 

 on some paper prepared with the bichromate 

 of potash and a weak solution of nitrate of 

 silver, exposed behind four coloured glasses, 

 blue, green, red, and yellow tints. M. Biot 

 is of opinion that there are difficulties inherent 

 in photographic pictures, which render the 

 object iUusire. M. Becquerel, on the other 

 hand, reports that he has obtained bright im- 

 pressions of the spectrum, and highly-coloured 

 drawings, on metallic plates, prepared with 

 chlorine. 



CoLOUEINa POETEAITS AND PlCTUEES.^ 



This is done upon the same system as minia- 

 ture painting, but the colours are used in a 

 dry powder. 



How Long oxraHT the Pictttee to bb 

 isr THE Camkea? — This is a point deter- 

 minable by practice, but in a good picture we 

 should see first the whites of the dress, then 

 the forehead of the sitter, and finally the 

 whole of the face and dress. The time of 

 exposure depends on the intensity of the light 

 and focal length of the lens in sunshine. 



Takin& Likenesses afteb Death. — An 

 American photographic firm announce that 

 they not only take portraits of the living, but 

 are prepared to take portraits after death. 

 Chaeles Matbtjet Aechee. 



THE GEOLOGY OF THE EIEESIDE— COAL. 



With shutters closed and curtains drawn 

 against the blasts of the winter's wind, we sit in 

 cheerful company around the homely hearth, 

 enjoying merry gossip, as the sea-coal fire 

 sends forth its cheerful blaze that makes our 

 faces ruddy. 



What stranger product of all the trea- 

 sures of our mother-earth than coal ? What 



countless years of manipulation has it under- 

 gone in the mysterious laboratory of Nature ! 

 What centuries of timber-growth, what ages 

 of forests have been exhausted in the accu- 

 mulation of its material ! How far back in 

 time did God's providence foresee the destiny 

 of man, and lay up almost inexhaustible stores 

 of fuel for his use P What would man be 



