VOL. XXXIX.] PHILOSOPHICAL TRANSACTIONS. (JjT 



they would have in an equal temperature of air; and one might, for this end, 

 chuse and agree on the heat of boiling water, as a fixed term, which, in all 

 appearance, will be the same all over the world. If the Royal Society should 

 approve this new construction of thermometers, and should order some of their 

 members to make the like, we might hereafter be able exactly to compare the 

 temperature of England with that of this country, and other places where the 

 like thermometers should be made. In order to reap this advantage from his 

 experiments, M. De I'lsle proposes to communicate to the Royal Society all the 

 observations he has made for 4 or 5 years past, on the barometer and thermo- 

 meter. M. De risle was informed, that 4 or 5 years since, the Royal Society 

 sent to M. Abraham Vater, at Wittenberg, large thermometers of spirit of 

 wine, made and regulated by an instrument maker of the Royal Society, to 

 compare the observations to be made in Germany, by means of those thermo- 

 meters, with the observations made in England by the like thermometers, the 

 one being regulated by the others. M. Weidler, professor of mathematics at 

 Wittenberg, mentions in the account which he gave of his meteorological ob-, 

 servations for the year 1729, that he has furnished himself with one, which he 

 intends to make use of hereafter for his meteorological observations. He also 

 says, that the observers of the Royal Society of Berlin make use of a like 

 thermometer; and M. De I'lsle had received from thence, observations on the 

 heights of the thermometer of spirit of wine, made probably with that instru- 

 ment, for the whole year 1729, and for the first 3 months of 1731. Those 

 observations are engraved on copper plates, where the heights of the spirit of 

 wine are expressed in parts of the French, English, and Rhinland foot. If 

 the Royal Society approve of this kind of thermometers, and are desirous he 

 should compare them with his; if they also desire that meteorological observa- 

 tions with those thermometers of spirit of wine should be made in Russia, he 

 begs you would send him several of them ; but then he begs that those sent 

 him may be well regulated, and exactly compared with those the observers of 

 the Royal Society make use of; supposing that some person of their body is 

 appointed to keep journals of these observations. M. De I'lsle will send in 

 exchange to the Royal Society, if they desire it, some thermometers of mer- 

 cury regulated by and compared with the four large ones he made at Peters- 

 burg, 



After this, M. De I'lsle inserted the last observations on the satellites of 

 Jupiter, which were made at Petersburg, since those inserted in the 3d volume 

 of the Memoirs of the Academy of Petersburg, to the present time, but are 

 omitted now, as of no use to repeat on the present occasion. 



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