1^3 On the Injxuence of the Sun 



Some celebrated philofophers, however, of the prefcnt 

 day have confidently believed, that if the variations of the ba- ' 

 rometer were carefully compared with the diflcrcnt poiitions 

 and diftances of the heavenly bodies, and particularly ot the 

 fun and moon, it would be found that many confiderable va^ 

 riations of the ftate of the mercury in the Torricellian tube 

 are eft'cfted by them. For, as the flux and rcHux of the fea 

 depend on the fun and moon, it cannot be doubted that in 

 the atmofphcre of the earth, which is much lighter than the 

 water of the fea, movements of the fame kind, which have 

 an influence on the barometer, muft take place. The firit 

 experiments on this fubje£l were made about fifteen years 

 ago by the celebrated Lambert, who employed for that pur- 

 pofe eleven years obfervations of the barometer made by 

 Doppelmayer of Nuremberg, and compared them vi-ith the 

 npogeum and perigeum.of the moon. He was not able, how- 

 ever, to obtain any certain refult, and confidered the period 

 of the obfervations as too fliort. 



Toaldo, who was furniflied with much more abundant 

 jnaterials, refumed the fubjeft, and by means of the forty 

 years obferva'.ions of the Marquis de Poleni and fon, with 

 eight years of his own, had a feries of fj^rty-cight years ob-. 

 fervations. After a laborious comparifon of thefe with 

 the apfidcs, fyzigies, and quadratures of the moon, and 

 with the pafl'age of the moon and fun through the iigns of 

 the zodiac, bethought he difcovered undoubted proofs of a 

 perceptible influence of the moon and fun on the barometer, 

 M. Frifi of Milan endeavoured to controvert this aucrtion, 

 which had been the refult of fo much labour, and maintained 

 that the variations of our atmofphcre have no limililude to 

 the flux and reflux of the fea, and can admit of no compari- 

 fon, as the latter is regular and invariable, the former only 

 temporary'. The flux and reflux of the fea, in regard to time 

 jind duration, are fo certain, that there are tables of them 

 for all the principal fea-ports, which never err; whereas the 

 variation- of the atmofphcre are at the fame time in differ- 

 ent places, and in the fame place at dift'erent times, fo 

 creat, that where it rains at one period for three or four 

 months it is fometimcs as long without rain. It fufflciently 

 appears at preftnt, from mathematical calculations, that 

 during the pafl'ige of the moon or fun, from the horizon to 

 the meridian,, the daily height of the baron>eter cannot be 

 changed more than .'^- of a line, Paris meafurc, by the eftetl 

 of the former, and abf)ut -■^-- by the effcd of the lattej*. 



To many, hmvevcr, Frifi's reafons did not app'^ar fo con- 

 plufive as to make them give over their rcfearches on this fub- 



