50 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1776. 



the top of the column of quicksilver in the tube. As this however would 

 frequently be attended with great inconvenience, the observer will often be 

 obliged to content himself with immersing it to a much less depth ; but then, 

 as the quicksilver in a great part of the tube will be of a difl^erent heat from that 

 in the ball, it will be necessary to apply a correction on that account to the heat 

 shown by the thermometer ; to facilitate which the following table is given, in 

 which the upper horizontal line is the length of the column of quicksilver con- 

 tained in that part of the tube wiiich is not immersed in the liquor expressed in 

 degrees ; the first perpendicular column is the supposed difference of heat of the 

 quicksilver in that part of the tube and in the ball ; and the corresponding 

 numbers in the table show how much higher or lower the thermometer stands 

 than it ought to do. The foundation on which the table is computed is, that 

 quicksilver expands one 1 1500lh part of its bulk by each degree of heat. 



' But as the generality of observers will be apt to neglect this correction, it 

 would be proper to form two sets of divisions on such thermometers as are 

 intended for trying the heat of liquors ; one of which should be used when the 

 tube is immersed almost to the top of the column ot quicksilver ; and the other 

 when not much more than the ball is immersed; in which last case the observer 

 should be careful, that the tube should be as little heated by the steam of the 

 liquor as possible. It must be observed however, that the heat of the liquor 

 may be estimated with much more accuracy by the first set of divisions, with the 

 help of the correction, than it can by the second set, as the latter method is just 

 orilv in one particular heat of the atmosphere, namely, that to which the 

 divisions are adapted; but if they are adapted to the mean heat of the climate 

 for which the thermometer is intended, the error can never be very great, and, 

 when the liquor is much hotter or colder than the air of that climate ever is, 

 will be much less than if the first set of divisions were used without any correc- 

 tion ; but, when the liquor is within the limits of the heat of the atmosphere, 

 greater accuracy will sometimes be obtained by using the lirsl set of ilivisions 



