ii6 Obfervations on thé Flu and Reflix 
rays by heating and rarefying it, in the ratio of its flrencth} 
according to the third of the Befode ahewniondd principles: 
That part, therefore, of the atmofphere which is gradually 
turned towards the fun, muft extend in proportion to the de- 
gree of heat which acts upon it; and rife above the reft; and 
this atmofpheric {welling will conftantly follow the apparent 
daily courfe of the fun: The moon, on the other hand, has 
no power to produce or change this phenomenon; becaufe; 
in all the experiments hitherto” made to collet aiid eoticens 
trate its rays, thefmalleit degree of heat has never been ie 
eerved. 
As there are therefore two different caufes, viz. the icihineth 
attraction of the fan and moon, and the heat of the fun 
alone; by which the latter, except at the time of the fyze+ 
gtes, when they both act in the fame direction upon oné 
- point, has a particular influence on the atmofphere of the 
earth independent on that of the former, it thence follows 
that they will produce three different fluxes every day: Two 
of them-arife from the attractive power of the fun and moon, 
and in their formation, direction, and movement, are per= 
feGtly fimilar to thofe produced 1 in the ocean from the fame 
caufes. The third, however, is produced by the heat of the 
fun alone; and its prominent parts will always be in’ that 
parallel through which the fun pafles in the courfe of his 
daily movement, .and will ome. follow that luminary, 
from parallel to parallel; at a fmall diftance. The two firft 
I thall call attraéion-tides, the third heat-tides. 
The tides of attraction, like thofe of the ocean, and froni 
the like grounds, have at the fame time, at two oppofite ends 
of the globe, projecting parts, and thefe lie almoft in that 
line which might be drawn from the centre of the earth to 
‘that of the moon. The heat-tides,-on the other hand, can 
take place only on one point of the globe; that is, m the 
point to which the fun is vertical. Their projecting part 
will be dire&ted towards that niesnihion and nearly follows 
its movement. 
In regard to the effe&s of thefe atmofpheric tides, they 
depend’on the natural ftate of the aérial fluid, and om its’ 
reft, which confifts in an equilibrium of all its parts. When 
this 
