cxxxvi GENERAL SUMMARY OF SCIENTIFIC AND 



recommends an angle of 35 for dry and 45 for balsam- 

 mounted objects. These prismatic slips can be cheaply and 

 easily made by grinding and polishing, say, a hundred at a 

 time, and will no doubt be brought often into use in decid- 

 ing whether certain appearances in the ordinary mode of 

 view are or are not illusory. 



In the April number of the American Naturalist is a de- 

 scription of a simple " spring clip" for use in mounting mi- 

 croscopic objects, the invention of Mr. N. N. Mason, of Prov- 

 idence, Rhode Island. 



We learn from a contemporary that in order to facilitate 

 the microscopical examination of the eye in cases of disease, 

 M. Monoyer has contrived a modification of Siebel's ophthal- 

 moscope, so arranged that three persons can make simul- 

 taneous observations. 



Dr. Golding Bird, in an article in the Quarterly Journal of 

 Microscopical Science, January, 1875, strongly advocates em- 

 bedding in elder pith for the purpose of making microscop- 

 ical sections. He employs for this purpose the pith of the 

 common elder; it is split longitudinally, and a small furrow 

 made with the finger-nail on the cut surfaces of each half, 

 somewhat corresponding in depth to the thickness of the 

 tissue to be cut, receives the specimen ; it is then placed in 

 the microtome, and put into water; in a few minutes the pith 

 will have swollen sufficiently to hold the specimen firmly in 

 its place, and the sections are made by means of a razor dip- 

 ped into spirit. 



Wenham's Reflex Illuminator. Mr. Samuel Wells writes 

 as follows to the Boston Journal of Chemistry, June, 1875 : 

 "I find that some immersion objectives are capable of trans- 

 mitting the extremely oblique rays that pass through the 

 illuminator so as to give a bright field when used on balsam 

 slides. In dry mounts the light can not be transmitted be- 

 yond the upper surface of the slide, but in balsam-mounted 

 slides the light passes to the upper surface of the cover and is 

 there totally reflected. If an immersion objective is adjust- 

 ed and connected with the cover by a film of water; the total 

 reflection will be destroyed, and the light will pass through 

 the cover and water into the front of the objective. The 

 ultimate direction of the ray of light after passing through 

 the illuminator is not changed by the introduction of the 



