PROCEEDINGS OF SOCIETIES. 281 



satisfactory results obtained witli appliances of the simplest kind. 

 The paper, which fully described the entire process of manipulation, 

 will be found printed at p. 250. 



A vote of thanks to Mr. Sanders for his paper was moved by the 

 President and carried unanimously. 



Mr. Wenham said he was glad to see this very important ques- 

 tion revived, and hojied that other persons might have their attention 

 drawn to it. When it was first brought out it was scarcely thought 

 worthy of consideration, and was altogether ignored as being useless. 

 He quite agreed with Mr. Sanders that there was nothing like sun- 

 light for the purpose. Those who practised the process would do 

 well to have their objectives supplied with a regular series of stops, 

 which would often be found advantageous ; by using the lowest stop 

 they would find that they would get much greater distinctness. He 

 also quite agreed with Mr. Sanders, that the apparatus employed 

 might be very simple ; he was often called upon to practise the process, 

 and found it so little trouble that he could arrange everything he 

 wanted for the purpose in half an hour. He enjoyed the luxury of a 

 dark room for it, but this might be done without, as Mr. Sanders 

 had shown ; he had a heliostat to direct the ray of sunlight through 

 the shutter into the room, and a piece of yellow glass up above would 

 let in light enough to work by. All that he required for taking the 

 pictures was within easy reach, and he was able to take them with 

 the greatest rapidity. He worked, in fact, inside his camera. The 

 heliostat which he used was an ordinary one, not one of the self- 

 moving ones, he would not be bothered by anything so troublesome ; 

 he placed it outside the window, and when its position required alter- 

 ing, he simply shifted it with his hand. 



The President said it was not strictly speaking a heliostat at all, 

 but merely a solar reflector to direct the beam into the room. 



Dr. Matthews inquired of Mr. Sanders how ho managed to procure 

 collodion for the purpose without " structure." 



Mr. Sanders said he found that the " structure" of the collodion 

 did not make any difference as to the results. 



Mr. Wenham noticed that in his paper Mr. Sanders mentioned 

 that he used very thin collodion, and in practice it was found that the 

 thinner the collodion the less " structure " it showed. 



The President asked for information as to the conditions on which 

 this reticulated " structure " depended. 



Mr. Wenham said he could not very well account for it, unless it 

 might possibly be some sort of form of internal crystallization. It 

 was found to be extremely regular. Like many other colloid sub- 

 stances, it had this tendency to break up into regular forms, like 

 artificial diatoms, or like Mr. Slack's silica films. 



Mr. S. J. Mclntire read a paper entitled " Notes ori Acarellus," in 

 which he described certain insects found parasitic upon Ohisium, and 

 closely resembling the Hypopus of the ' Micrographic Dictionary,' and 

 the insect mounted by Mr. Topping under the name of " Parasite of 

 House Fly." The paper was illustrated by drawings and by specimens, 

 both alive and mounted, exhibited under microscopes in the room. It 



