76 WISCON'SIIT ACADEMY SCIENCKS, ARTS, AND LETTERS. 



tion of the scale of the instrument used, the result might be taken 

 as a test of the accuracy of the formula. 



Whenever observations are made in a room of moderate tem- 

 perature, the detached thermometer should be placed in the open 

 air in a sheltered place, and from the temperature obtained the cor- 

 rections for dilation may be made with accuracy, for expansion of 

 mercury, the temperature as shown by the attached thermometer 

 must necessarily be taken for corrections of the same. 



The barometer is subject to regular periodical oscillations in con- 

 sequence of variable temperature of the earth and the consequent 

 air currents. A very small diurnal barometric wave exists which 

 may be traced with great accuracy. The laws which control the 

 regular motions will soon be thoroughly understood from the re- 

 sults of a recording apparatus in use for the several years by which 

 a diagram is photographed which gives an accurate continuous, 

 record day or night. 



The thermo-barometer and other useful and interesting matter 

 is omitted for want of the time necessary to prepare the same. 



