■yo Microscopical Essays. 



brafs tube, which contains the lenfes for condenfing the light, and 

 throwing it upon the object; there is a fecond tube within that, 

 marked 9 and 10, which may be placed at different diftances 

 from the objecl; by the pin 1 1« 



jP When this ftage is ufed as a fingle microfcope, without any 

 reference to the lucernal, the magnifiers, or objecl; lenfes, are to 

 be fcrewed into the hole 12, and to4>e adjufted to a proper focus 

 by the nut 13. 



N. B. At the end A B of the wooden body, there is a Aider, 

 which is reprefented as partly drawn out at A ; when quite taken 

 out, three grooves will be perceived, one of which contains a 

 board that forms the end of the box, the next contains a frame 

 with a greyed glafs, the third, or that farther! from the endAB, 

 two large convex lenfes. 



Of the Lamp. 



Fig. 3, reprefents one of Argand's lamps, which are the moft 

 fuitable for microfcopic purpofes, on account of the clearnefs, 

 the intenfity, and the fteadinefs of the light. The following ac- 

 count of the method of managing them, with other obfervations, 

 is copied from an account given by Mr. Parker with thofe he fells. 



The principle on which the lamp acls, confifts in difpofmg 

 the wick in thin parts, fo that the air may come into contact with 

 all the burning fuel, by which means, together with an increafe 

 of the current of air occafioned by rarefaction in the glafs tube, 

 the whole of the fuel is converted into flame, 



6 The 



