PROCEEDINGS OF THE SOCIETY. 383 



horizontal] plates, the upper one capable of vertical movement, though 

 always remaining parallel to the lower one. The specimen to be 

 mounted was placed face downwards on the lower plate ; a glass slip 

 was carried by the upper plate, which had a large hole in it through 

 which the back of the specimen could be seen. Having obtained the 

 proper position the irregular back surface of the specimen was filled up 

 with some suitable mounting medium, the upper plate being then 

 lowered until the glass plate pressed firmly upon it. The two plates 

 were then clamped together until the medium had set. In this way the 

 specimen was attached to the glass in a position which ensured that the 

 polished surface was exactly parallel to the surface of the slip. A piece 

 of washleather tightly stretched upon the lower plate avoided all risk of 

 the polished metal face getting scratched during the process. 



The third exhibit consisted of glass troughs designed by Mr. 

 Kingsford for use as aquaria for infusoria, or for containing coloured 

 fluids to act as light filters. They were formed of two circular plates of 

 glass held firmly by a metal band lined with india-rubber, and kept in 

 position by binding screws. A sufficient opening at the top was pro- 

 vided for the introduction of liquids. The great advantage of this form 

 of apparatus is that it can be taken to pieces with facility for the pur- 

 pose of cleaning or for replacing the glass if broken. 



Mr. Kingsford said that another merit of these troughs was that they 

 would stand any variations of temperature without becoming leaky. 

 To test this he had repeatedly boiled water in one, and after pouring 

 this out had immediately filled up the cell with cold water, and found 

 that it showed no signs of leakage afterwards, neither was the glass 

 cracked. 



Mr. A. A. C. E. Merlin's note on Mr. Nelson's new formula Amplifier 

 was read by the Secretary. 



Mr. Karop said that, so far as he understood from the paper, the 

 method appeared to be the principle of the Barlow lens applied to the 

 Microscope, viz. a negative lens interposed between objective and ocular 

 to increase the magnification. This device was not, he believed, a success 

 in the telescope, but of course might very well be so for the purpose 

 intended here. 



The thanks of the Society were voted to Mr. Merlin for his com- 

 munication. 



• ' Mr. E. M. Nelson's paper upon the visibility of Mr. Grayson's rulings 

 of 120,000 lines to the inch was read by the Secretary. 



The President thought this was a very interesting communication. 



Dr. Hebb remarked that he saw this plate exhibited at the recent 

 conversazione of the Royal Society, and though it was easily resolved, 

 his impression was that some of the lines were more strongly marked 

 than others. 



Mr. E. E. Hill pointed out that the ruling shown at the Royal 

 Society was only under an objective of 1 • 1 numerical aperture. 



The thanks of the Society were voted to Mr. Nelson for his paper. 



