i70 



PHILOSOl'HICAL TRANSACTIONS. 



[anno 1777- 



yet it is at least as much so as a thermometer adjusted in the latter method can 

 be; so that this double set of divisions possesses all the advantages which can be 

 expected from that method of adjusting thermometers, without the inconve- 

 niences. 



A Table for correcting the observed Height of a Thermometer, ■whenever the Quicksilver in the Tube if 



not of the same Heat as that in the Ball. 



To make use of this table, in the left-hand perpendicular column look for the 

 number of degrees contained in that part of the tube which is not immersed in 

 the fluid whose heat is to be tried, and in the upper horizontal line seek the sup- 

 posed difference of heat of the quicksilver in that part of the tube from that in 

 the ball ; the corresponding number in the table is the correction, which must 

 be added to the observed heat when the quicksilver in the tube is cooler than that 

 in the ball, and subtracted when it is warmer: for example, let the observed heat 

 of the fluid be 475°, let the thermometer be immersed in the fluid as far as to 

 the degree of 25", or to that part of the tube which should be marked "25° if the 

 divisions were continued long enough; then is the number of degrees in that 

 part of the tube which is not immersed in the fluid 450; and let the heat of the 

 quicksilver in that part of the tube be supposed lOO"; and consec|uently the dif- 

 ference of heat of the quicksilver in that part of the tube from that in the ball 

 375; then in the left-hand perpendicular column seek the number 450, and in 

 the upper horizontal line the number 375; the corresponding number in the 

 table, or the correction, is 15°, and therefore the true heat of the fluid is 4c)0°. 



This correction may be had very easily without the help of the table, only by 

 multiplying the number of degrees not immersed in the fluid by the supposed 

 difference of heat, dividing the product by 10000, and diminishing the quotient 

 by -jr part of the whole. 



In the following pages we have thrown together the practical rules, which we 

 would recommend to be observed in adjusting the tlxcd points of thermo- 

 meters. 



