libS /Vie Microscope. 



prisms, alum into octagons, crystals of nitre, saltpetre, and green 

 vitriol into the same form. To obtain crystals of camphor, 

 place a drop of spirits of wine on a glass, hold it over a candle; 

 when evaporated, place it on the microscope, and they will be 

 seen.' 



To FIND THE Magnifying Power uf the Microscope. 

 Place a micrometer upon the stage, (one of the two-hundredths 

 of an inch will be the most useful for this microscope,) and ad- 

 just it to the focus of the power in use. In order to ascertain how 

 many limes the squares are magnified, no more will be necessary 

 than to ascertain the size of the magnified image of one of them, 

 and the best method to do which is the following: — on several 

 pieces of card rule a few squares which bear a known proportion to 

 an inch, beginning at about three-quarters of an inch; and decreas- 

 ing very gradually, until you arrive at a tenth of an inch. The 

 use of these pieces of card h exemplified by the following exam- 

 ple. 



Suppose the lowest power to be in use, with the above mi- 

 crometer upon the stage, adjusted to the true focus, compare 

 the squares upon several of the pieces of card, and select that 

 which contains squares of the same size as the magnified image; 

 and having previously noted upon each piece of card the propor- 

 tion each square bears to an inch, you immediately know the size 

 of the magnified image, which in this instance is indicated by the 

 card to be a tenth of an inch; and as the two-hundredih of an 

 inch is contained twenty times in the tenth of an inch, so many 

 times is the length of an object magnified; and as the breadth is 

 magnified in the same proportion, the square of twenty must be 

 taken, which is four hundred, the true magnifying power. 



The following are the different magnifying powers of the mi- 

 croscope. 



No. 1 , the lowest power magnifies 



No. 2, second power ditto 



No. 1 4" 2 combined together, 3d power. 



No. 3, fourth power ditto . . 4225 26,000 



Other powers may be added to this microscope as described 

 in the table. 



N. B. The height of an object being magnified in the same 

 proportion as the length and breadth, the cubes of the magnified 

 diameters might be introduced in the above scale, although it 

 must be admitted, that the height is, in a great measure, lost to 

 the eye, in consequence of its being perpendicular to the object; 

 therefore, in estimating the magnifying power, the cube is usually 

 f ejected. 



Single. 



100 



With the Com- 

 pound Body. 



625 times. 



144 



900 



400 



2500 



