Cambridge Philosophical Society, 459 



March 15. — Professor Miller made a communication on different 

 improvements in the Reflective Goniometer ; and a description of a 

 New Reflective Goniometer. 



Professor Stokes concluded a paper on the Composition and Reso- 

 lution of Streams of Polarized Light from diff^erent Sources (see the 

 abstract under the date Feb. 16, 1852, Phil. Mag. vol. iii. p. 316). 



He also made a communication on Haidinger's Brushes. 



Also on the Optical Properties of a New Salt of Quininfe. The salt 

 alluded to is that which had recently been discovered by Dr. Herapath 

 (Phil. Mag. vol. iii. p. 161). The substance of this communication 

 formed the subject of a notice of the properties of the salt which the 

 author read at the Meeting of the British Association at Belfast, 

 which will be found in the Report of the Transactions of the 

 Sections. 



April 26. — The Rev. Mr. Kingsley gave an account of the appli- 

 cation of Photography to the Microscope. 



The earliest attempts in photography were directed both by Sir 

 H. Davy and Mr. Fox Talbot to the fixing upon prepared paper the 

 images of objects by the solar microscope, and the latter gentleman 

 succeeded completely, as far as his instrument allowed, in obtaining 

 pictures of minute structures. Shortly after the publication of Mr. 

 Talbot's process, various attempts were made to apply the oxyhy- 

 drogen microscope to the same purpose, as that instrument had 

 superseded the solar. The result however was, that it was aban- 

 doned on account of the great time that was found to be necessary 

 for impressing an image ; and after a great variety of trials by Prof. 

 Owen, Dr. Carpenter, Dr. Leeson and others, the use of the instru- 

 ment for this purpose was given up. 



The discovery of the collodion process, so much more sensitive 

 than that of Mr. Talbot, led the author to think, as soon as he be- 

 came acquainted with it, that we were in possession of the means of 

 impressing microscopic objects by means of artificial light without 

 any great trouble. A friend of his had an oxyhydrogen microscope 

 of the common form, and on making a trial with it, he found that 

 by using a very sensitive kind of collodion, he could obtain images 

 by about a minute's exposure. On examining the instrument, how- 

 ever, he saw that its form must be completely changed, in fact, that 

 an entirely new kind of instrument was required to obtain the best 

 eiFect. The two points to be regarded as the peculiar principles of 

 this microscope are, 1st, that none of the radiant light be lost, or as 

 little as possible ; 2ndly, that the magnifying power be obtained by 

 such means as would not place the screen for receiving the image 

 beyond such a distance from the object, that the motions of the 

 instrument could be governed at the same time that the image 

 was closely inspected. The first of these objects is secured by giving 

 a very large angular aperture to the system of lenses used for col- 

 lecting the light, and by using another set of lenses for condensing 

 it again on the object, and so arranging their focal length in pro- 

 portion to the focal length of the object-glass, as to cover the plate 



3H3 



