PROCEEDINGS OF THE SOCIETY. 559 



Mr. Ciirties inquired if any special means were adopted in plioto- 

 grapliing tlie opaque objects. He thought it must be admitted that 

 they had been extraordinarily well shown, their sharpness of detail 

 being such that he had supposed they must have been taken by the 

 electric light. 



Mr. Smith said that there was nothing unusual about the process 

 in any way, it was simply a question of manipulative skill. Some of 

 the transparent objects were illuminated by the spot-lens, and ordinary 

 objectives were used. 



Mr. Crisp said that for the next number of the Journal he had 

 written a note on the question whether photographs of microscopic 

 objects were better for purposes of class illustration than the objects 

 themselves thrown on the screen, and had expressed himself in favour 

 of the natural objects. What, however, he had seen that evening 

 certainly required him to alter his opinion. 



Mr. Smith in reply to an inquiry as to what kind of lantern 

 apparatus had been used for showing the slides upon the screen, said 

 it was the ordinary form of lantern known as the Sciopticon, the 

 illumination being by a jjaraffin oil lamp with a double burner. It 

 was very simple to use, did not produce an unusual amount of heat, 

 and held enough oil to burn well for several hours. A dissolving 

 apparatus was added for the purpose of changing the slides. 



Dr. Millar asked how the slides were prepared ; were they printed 

 upon the glass ? 



Mr. Smith said that in the first instance a photographic negative 

 was taken in the usual way ; this negative was upon a glass plate, 

 and was so called because all the lights and shadows were reversed 

 from what they were in the natural picture. From this negative an 

 ordinary photograph was produced by printing from it in the usual 

 way. The Woodbury-type process made use of the property acquired 

 by gelatin when mixed with bichromate of potash, in virtue of which 

 it became insoluble after being exposed to the action of light. A 

 film of gelatin, so prepared, had the photograph placed upon it and 

 after being exposed to light was washed in hot water which dissolved 

 away those parts which the light had not affected. In this way a 

 very delicate film was obtained not exceeding the 1/300 in. in thick- 

 ness, but containing every line of the picture in relief. This film 

 was put upon a steel plate, and a piece of lead having been placed 

 upon it, they were subjected to a pressure of many tons weight, by 

 which means an intaglio mould was formed upon the lead. The 

 plates were practically casts from this mould made in gelatin and 

 darkened with lampblack. 



The President was sure he should be doing what would commend 

 itself to the whole meeting, in projjosing a vote of thanks to Mr. 

 Evans and his colleague Mr. Smith, for the very interesting exhibition 

 for which they were indebted to them, and upon the success of which 

 they were to be very heartily congratulated. 



The thanks of the meeting were tlien unanimously voted to Mr. 

 Evans and Mr. Smith. 



