THE MICROSCOPE. 51 



This, being an imperfect polish, radiates the light as if it were self- 

 luminous. Now, all light reaching the bottom of the slide at a 

 greater incidence than the critical angle will be reflected upwards. 

 This goes in all directions and such as may go towards the lens will, 

 to some extent at least, enter, after having passed through the 

 diatom. 



This is shown in the diagram where a represents the front of 

 the objective, b the slide and cover, (balsam mount, of course, and 

 hence regarded as one substance), c the object and d the homo- 

 geneous fluid. The dotted lines show the course of the light, going 

 in the directions indicated by the arrows. 



So it will be seen that so far from being central light, it is only 

 light in excess of the numerical value 1.00 that really does the work. 

 That the light really takes the course I have pointed out I have 

 proved by painting the lower surface of the slide with India ink as 

 shown by the heavy lines in the diagram. Then the only course 

 left is that described. 



I think Mr. Edward Bausch was the first to resolve Am. pel. by 

 this method, and since then it has been done by several persons and 

 by various objectives. All that is necessary, so far as the objective 

 is concerned,, is that it be capable of resolving it by oblique sun- 

 light and have a sufficiently broad front to radiate the light. 



PROJECTING LANTERNS. 



BY C. H. STOWELL. 



A GOOD deal has been said of late about projecting lanterns, 

 and some new styles have been brought forward for public 

 favor. One inventor has a lantern that "will actually show the cir- 

 culation of the blood in the frog on a disk four feet in diameter." 

 So much has been said that no apology is necessary if I describe 

 my own lantern and what it will do. 



After experimenting for over two years, I purchased a Marcy's 

 lime light sciopticon about five years ago. One of Zentmayer's 

 microscopic attachments was ordered at the same time. Two cylin- 

 ders, filled with oxygen and hydrogen, respectively, were purchased 

 from New York. For objectives I have used those from my micro- 

 scope with success, although the field is flatter and lighter if 

 objectives be used that were made especially for this work. Zent- 



