46S Scientific InfeUierence. [Junb, 



room for it in tlie Annals of Philosophy/. My method is as 

 follows : — 



1. Provide a quantity of mercury more than sufficient to fill the 

 tube to be graduated. Take its specific gravity with great care ; let 

 us suppose it to be 13"399. 



2. Suppose our object is to graduate the tube into lOOths of a 

 cubic inch. At the temperature of 60° the lOOth part of a cubic 

 inch of pure water weighs 2*525 grains troy. The lOOth part of a 

 cubic inch of our mercury weighs 2-525 x IS'SDO = 33*83 

 grains. 



3. Weigh out 33*83 grains of mercury with all possible accu- 

 racy. Put it into a small glass capsule. Prepare a glass tube, 

 about a foot in length, almost capillary in the bore, open at both 

 ends, and terminating at one extremity in a point. Apply your 

 mouth to the upper extremity of this tube, and draw into it the 

 whole of the mercury which you have weighed out, taking care 

 that it fills the lower part of the tube exactly without leaving any 

 vacuity. Before you remove your tongue from the upper orifice of 

 the lube, apply your finger to the lower orifice, and then with the 

 edge of a small triangular file mark on the tube the upper surface 

 of the mercury. The bore of the tube should be so fine that the 

 iriercury ought to occupy about three inches in length. This mea- 

 sure being thus made, the principal part of the labour is over. 



4. Take a slip of writing paper about ith inch in breadth, and 

 as long as the tube. Apply guin water to one side of this slip, and 

 paste it on the tube, \vrapping round it a piece of twine from one 

 end of the tube to the other, so as to keep it firmly fixed in ,its 

 |)lace. Set it aside till the paper be quite dry, then remove the 

 twine; for the paper will now adhere firmly to the tube. 



5. Place the tube in a perpendicular direction, upon a table, 

 with its open end uppermost. Put the mercury whose specific gra- 

 vity you have determined, into a cup. Draw into your tube, pre- 

 viously graduated as a measure, a quantity of mercury, till it 

 stands exactly at the mark on the tube. Pour this quantity into 

 the tube, and let an assistant draw a pencil mark upon the paper, 

 corresponding with the upper surface of the mercury. Pour in a 

 second measure of mercury, and mark its surface on the paper 

 with a pencil line as before. Proceed in this way till you have 

 filled your tube; and a little practice will enable you to proceed 

 with great dispatch, wiihout any diminution of precision. 



G. You have now your tube graduated by pencil lines drawn on 

 the slip of paper pasted to it. Take a fine triangular file, moisten 

 one of its edges so as to enable you to cut through the paper with- 

 out using any violence. Cut through the first pencil mark, and by 

 drawing the file along the tube you easily make a fine and distinct 

 line on the tube exactly under the pencil mark. Cut in this way 

 through all the pencil marks, and make every filth and tenth divi- 

 sion twice as long as the others. In this way y(;u may cut through 

 all the pencil marivs iti a few niinutes, and when the paper is le- 



