Microscopical Essays* 



133 



Ian thorn, made fomething like the common magic lanthorn, fit 

 to contain one of Argand's lamps.* The lanthorn mould have 

 an aperture in the front, that may be moved up and down, and 

 capable of holding a lens ; by this a pleafing uniform denfe light 

 may be eafily procured. The lamp mould move on a rod, that 

 it may be readily elevated or depreffed. The lanthorn may be 

 ufed for many other purpofes, as for viewing of pictures, ex- 

 hibiting microfcopic objects on a fereen, &c. 



Many tranfparent objecls are feen beft in a weak light ; among 

 thefe we may place the prepared eyes of flies and animalcula in 

 fluids ; the quantity of light from a lamp or candle may be 

 leflened by removing the microfcope to a greater diftance from 

 them, or it may be more effectually leffened by cutting off a part 

 of the cone of rays that fall on the object, either by placing the 

 cone, Fig. E, Plate IX. under the Mage, or by forming circular 

 apertures of black paper, of different fizes, and placing either 

 a larger or final ler one on the reflecting mirror, as occafioa 

 may require. 



There is an oblique fituation of the mirrors, and eonfequently 

 of the light, which is eafily difcoveredby practice, but for which 

 no general rule can be given, that will exhibit an object more 

 beautifully and more dift in&Iy than any other pofition, (hewing 

 the furface, as well as thofe parts through which the light is. 

 tranfmitted. 



4 better 



* The lamp {hould not be of the fountain kind, becaufe the rarefa&ion of the 

 air in the lanthorn will often force the oil over. 



