CHAPTER IV. 



MANIPULATIONS WENHAM'S REFLEX ILLUMINATOR. 



This instrument, and its various modifications, having 

 come into very general use in this country, we give the 

 following cut and description, taken from Dr. Carpen- 

 ter's work on " The Microscope and Its Revelations:" 



"A very ingenious and valuable illuminator for high 

 powers has been recently devised by Mr. Wenham, and 

 constructed by Messrs. Ross. It is composed of a glass- 

 cylinder, half an inch long and four-tenths in diameter, 

 the lower convex surface of which is polished to a radium 

 of four-tenths. The top is flat and polished. Starting 

 from the bottom edge, the cylinder is worked off to a 

 polished face at an angle of 64 ; close beneath the cylin- 

 der is set a plano-convex lens of IJ-inch focus. When 

 parallel rays are thrown up through this apparatus from 

 the mirror, they impinge on the upper surface of a glas& 

 slide at an angle of total reflection ; but if a suitable 

 object adhere to that surface, the light reaches it on an 

 angle that admits its passage. The object is then seen 

 brilliantly lit up upon a dark ground, and many fine 

 markings, that escape notice with other methods, become 

 very distinct. It is advisable to rotate the apparatus 

 until the best position is obtained. Some skill and 

 practice are required to use this apparatus to advantage, 

 but it will amply repay the trouble of mastering its 



