Mr Guthrie oji the Single Reflecting Microscope. 3J27 



having a part of it screwed, and having a milled-nut c upon it. 

 Let the pivots ab of the spindle be transferred to the holes a b 

 Fig. 2, with one of the columns passing through the hole e of the 

 segment, and the instrument is completed. 



To use the microscope, let the instrument be placed on the 

 instrument J7^, and let that instrument be so placed that the ob- 

 ject shall be in the axis of the speculum, or, which is the'' same 

 thing, that its image be in the field of view ; and let the spindle 

 be turned in any way necessary for the perfect adjustment of 

 the focus, by the friction of the finger upon the milled-nut of 

 the spindle, which thus causes the object traverse in the axis 

 of the speculum, and the focus is thus adjusted with the utmost 

 precision. 



Instead of having the tube ABCD, Fig. 1, all in one piece, 

 the instrument is much improved by having it in sections to 

 draw out of one another, as shewn in the figure. It thus gives 

 different degrees of magnifying power by the same eye-glass, in 

 proportion to the length to which it is drawn out. And when 

 it is shut up, the tubes, by covering the speculum, render the 

 instrument quite portable. 



The magnitude of the image, compared to that of the object, 

 is in the proportion of their respective distances from the specu- 

 lum ; therefore, by dividing the distance IH, Fig. 1, by the dis- 

 tance OH, and multiplying the quotient by the magnifying 

 power of the eye-glass, * the magnifying power of the instru- 

 ment is obtained. 



Notice of some minute Calculi found in the Urinary Bladder 

 of an Ox. By John Davy, M. D. F. R. S., Assistant-In- 

 spector of Army Hospitals, &c. Communicated by the 

 Author. 



The calculi of which I propose to give a short account, were 

 presented lately to the Museum of the Medical Department of 

 the Army by Dr Williams, Surgeon of the 68th Regiment. 



• The magnifying power of the eye-glass is found by dividing eight inches 

 (the distance of the object from the eye in perfect vision), by the focal dis- 

 tance in inches of the eye-glass. 



Y 2 



