S6 CORRECTION OF THE HEIGHT OF THE BAROMETER. 



Central depression. Maiginal 



t ■ /v — ■■ — \ depression. -..«• 



Diameter. nn - i^VoSrve.. by ' nnK DifFerer.ce. 



l'OO '00031 -00032 



'90 '00000 V)006'2 



•SO -00115 -001 IS 



•70 '00220 -00 224 



•60 -00411 -00^16 -005 -0637 '0596 



•50 "00799 -00805 -007 -0676 -0596 



•45 '01100 '0110(5 -0690 "0580 



•40 '01516 -01522 -015 '0714 -0562 



•35 -02093 '02098 '025 '0745 '0536 



•30 '02902 *0290t> '036 '0787 '0497 



*25 '04064 '04067 '050 -0850 -0444 



•20 -05800 -05802 '067 '09C6 -0386 



•15 -08620 -08621 -092 '1171 '0309 



•10 -14027 -14027 '140 'l6l9 '02l6 



•05 '29497 -29497 '3060 -0110 



Illation ot When it is required to continue the curve till it becomes 

 perpendicular to the absciss, it is evident that the series 

 cannot be sufficiently accurate, since in this case the least 

 imaginable increase of the absciss would afford an impossi- 

 ble value for the ordinate. It is therefore convenient to 

 compute the value of b and y for a portion of the curve a 

 little less than that which is required, and to determine the 

 length of the remainder from its mean curvature, deduced 

 from the magnitude of the ordinate, together with that of 

 the absciss. For example, if it be required to find the cen- 

 tral and marginal elevation of the surface of water contained 

 in tubes 1 inch, f, and 1 of an inch in diameter, taking 

 m ~ -01; we may continue the curve till its inclination to 



the horizon becomes 60°, and — = '866 ; but we must first 

 m 



determine the corresponding diminution of the diameter, 

 in order to obtain the value of x. For this purpose the part 

 of the curve wh.ch is nearly vertical may be compared with 

 a cubical parabola, the distance of which from its tangent 

 is to. the versed sine of the osculating circle, as the distance 

 from the vertex, diminished by one third of the tangent, to 

 the whole distance. In the first example, taking the mar- 

 ginal elevation by conjecture *15, we must deduct '02, the 

 height corresponding to the horizontal curvature, of which 



the 



