88 THEMICROSCOPIST. 



place, with one of the three dark wells or stops, p, p'ip"i which 

 will make a dark background. If the objects are mounted on 

 circular discs, g, the well will not be needed. 



The object-glasses comprise four powers. No. 3 and No. 4 

 have the tube of their front lens movable, for adjusting their 

 performance with objects either uncovered or covered with thin 

 glass. The graduated screw collar, by which the adjustment is 

 made, is seen at 5. 



The high price of these instruments must necessarily put 

 them out of the reach of those whose means are limited, and 

 our opticians seldom import them, except to order. Of late, 

 however, a praiseworthy effort has been made to simplify the 

 construction of the mechanical parts, so as to bring the price 

 within the control of the generality of medical men and other 

 students of nature. Mr. J. B. Dancer, Manchester, England, 

 furnishes a very complete microscope, with two object-glasses 

 and the necessary apparatus, for 10. Messrs. Powell and 

 Lealand have also fitted up an instrument with a stand of cast- 

 iron, whose cost, exclusive of the object-glasses, is 9. Other 

 manufacturers are also pursuing the same course. 



From the cause above referred to, the majority of micro- 

 scopes used in this country are of French or German manufac- 

 ture. Chevalier and Oberhauser have furnished some excellent 

 instruments; but the mechanism not allowing the mirror to 

 turn aside from the axis of the instrument, so as to give a side 

 light, is a serious objection to them, although the optical part 

 is often very little inferior to the English. 



Dr. Bennet, of Edinburg, highly recommends Oberhauser's 

 instruments to medical men. He advises the employment of 

 the No. 3 and No. 7 object-glasses, answering to the i inch 

 and 1 inch lens of the London opticians. 



Hitherto, the fashion in this country in regard to microscopes, 

 has led to the almost universal employment of high powers, to 

 the neglect of the others, so that it is exceedingly difficult to 



