o Standard of Weight and Meafure. %t% 



flung in another cradle, part of which is feen zt g b h /, fupported by four wires from the 

 pointy. 



In fig. 7, is feen a fphere of brafs, </, fix inches in diameter, flung in a cradle, »b c,hj three 

 wires*, from the Hnlcs f, fufpended in a glafs jarf, containing near four gallons of water, 

 whofe temperature is fhewn by a thermometer at e. 



§ II. It was necefl'ary to meafure the exa£t fize and corre£lnefs of figure of this (phere.; 

 For this purpofe was made a wooden gauge or frame a b c d e (Plate V. fig. 2), in which the 

 fphere was placed upon femicircular pieces, within-lined with green cloth to prevent bruifing 

 it ; upon this frame was placed a brafs fquare k / mn, whofe fides were about , ^o inch in 

 length more than the diameter of the fphere. This fquare, b/ raifing or lowering the fcrews 

 or s, was eafily made to coincide with a plane palling through • the centre of the fphere. p 

 is a micrometer fcrew, the interior extremity of which is brought juft to touch the furface 

 of the fphere, while the oppofite fide bears gently againft the interior fide of the frame at ; 

 and by turning the fphere round fo as to prefent different diameters to thefe points of contaft, 

 any variety in the diameter may be feen by the index / and plate q divided into io,oooths 

 inch. To render this operation more convenient, three great circles were drawn with a 

 pencil upon the fphere, at 90° diftance from each other (the two former were traced by the 

 artift in the lathe, while the fphere was making, and the third was drawn from them), and 

 each was divided into 8 equal parts. The immeJiate refult of thefe experiments would only 

 give the differences, and not the abfolute quantity of the diameter } for this purpofe, a brafis 

 ruler, r, fig. 3, was made of fuch a length as jufl to go within the brafs frame k Im n; and 

 being fubflituted in the place of the fphere, could eafily be compared with any given diameter, 

 and afterwards meafured with the divided fcale, fig. i. With thefe inftruments I made the 

 following obfervations, Auguft 31, 1796, the thermometer being at 61°. 



§ 12. Examination of the dimenfions of the brafs cube, by means of the divided fcale. 



The microfcope and micrometer being both adjufted, as well with refpedl to their focus t 



• Thefe wires were of fuch a fize that 91 inches weighed 20,7 1 grains, confequently i inch=o,2276 grain, 

 and the three wires=o,6S28 grain; and their fpccific gravity being 8,7, their lofs of weight by iinkine i 

 inch in water, would be 0,0785 grain. This correftion it may be neceffary hereafter to attend to. 



t The glafs j,ar is made fomewhat conical, being in 



Inches. 



Diameter at top 11,0 



Ditto at bottom t,7 



Mean ditto 10,35 



Mean height within 11,8 



Contents in cubic inches .... 991,78 



Which is in ale. gallons . . . =3,8^151 quarts. 

 It may alfo be noted, that one inch in depth of the water near the top is =1 ij cubic inches, which is equal 

 to the exaft bulk of- the fphere, as will be feen hereafter; 



Inches. 



I The focal length of the obje£t lens is :=o,75 



The diftance of the crofs-wires from the objeft lens :=z,oo 



The focal length of the combined eye-giafs =1,50 



Whence the magnifying pewer of the micrcfcope becomes .... = 14,* times. 



as 



