Chase.] 



406 



[July. 



tides exclusively to " the rotation of the earth, combined with its 

 revolution about the sun," attached too much importance to the sim- 

 ple combination of the motions of rotation and orbital translation, but 

 his mistake is no greater than the opposite belief, which is now too 

 prevalent, that there is only a single influence which can produce 

 any important tidal eifects in the atmosphere. 



In a former communication on the rotation-tide, I deduced " from 

 a reference of the aerial motions to a supposed stationary earth, a law 

 of tidal variation nearly identical with the law that is derived from a 

 consideration of the relative attractions of two bodies revolving about 

 their common centre of gravity."* That such should be the ease, 

 might have been reasonably expected from the dependent connection 

 of rotation and revolution with gravity and inertia. 



I was therefore led to believe that the daily lunar barometric tides 

 might be indicated by an expression of the same general form as the 

 monthly lunar and daily rotation tides. On investigation I am gra- 

 tified at finding that such is indeed the case. If M is the barometric 

 mean for any given day and place, and ff is the moon's altitude, ob- 

 servation and theory concur in demonstrating that the lunar tide may 

 be expressed by M C (sin. d cos. d),-f C being a constant to be de- 

 termined for each station, the principal elements of which are func- 

 tions of the latitude, of gravity, and of time. I subjoin, in illustra- 

 tion, a 



TABLE OF THE AVERAGE DAILY LUNAR BAROMETRIC TIDES. 



* Thi.s is evidently only another form of a single element in La Place's law of 

 the tides. I present it in this shape, both because I obtained it independently, 

 and becau!?e it makes the resemblance to my rotation formula more striking. 



t Major-Ueneral Sabine's table of the lunar tides at St. Helena, from October, 

 184.3, to September, 1845 (Phil. Trans., 1847, p. 48), gives for the ratios of the 

 MEAN, .497, .8.32, and 1, which, if aver.aged with the mean at Girard College, 

 gives a general mean of .512, .858, and 1. The grand mean for the entire pe- 

 riods of observation at the two stations is .500, .849, and 1. 



