l68 PHILOSOPHICAL TRANSACTIONS. ^ [aNNO 1715. 



is to be observed, that the air in the inner parts of the mine, where I made 

 these experiments, was rarefied by a fire, that was kindled there the day before, 

 and the place had a moderate warmth like a stove. 



Note. — It was found by several experiments made before the Royal Society of 

 London, that the elastic forces of compressed air are directly as the compress- 

 ing weights; and by Dr. Scheuchzer's observations it is evident, that the same 

 ratio holds very nearly in rarefied air. For though there be found some differ- 

 ence, yet it is not so considerable, but that it may easily arise from the inequa- 

 lity of the diameter of the tube. That these experiments may be duly per- 

 formed, the capacity of the tube must be divided into equal parts, by pouring 

 into it an ounce of mercury only at a time, instead of dividing its length into 

 equal parts, 



Botanicum Hortense IV, ^c. &c. By James Petiver, F. R. S. Continued from 

 the last Tramactiom. N° 344, p. 269. 



Observationes Ccelestes Britannia^, Grenovici in Observatorio Regio habitce, 

 ^nnol7l3. By Mr. Flamsteed. N° 344, p. 285. 



These celestial observations are of the planets Saturn, Jupiter, Mars, the 

 Moon, and the satellites of Jupiter. But omitted here, as given more complete 

 in the author's Historia Coelestis. 



Of an Experiment made by Dr. Brook Taylor assisted by Mr. Hawhsbee, in 

 order to discover the Law of the Magnetical Attraction. N° 344, p. 294. 



By order of the Royal Society, Mr. Hawksbee and myself made an experi- 

 ment with the great loadstone belonging to the Royal Society, in order to dis- 

 cover the law of the magnetical attraction; and not long after I gave an account 

 of it to the society in a letter to Dr. Sloane, (who was then secretary) dated 

 June 25, 1712. Since that, Mr. Hawksbee made another experiment of the 

 same nature with a smaller loadstone; which he has given an account of in the 

 Phil. Trans. N^ 335. But on comparing the numbers of that experiment with 

 those of the other, I find the numbers of the first experiment to be much 

 more regular. I therefore conclude that to be the best experiment, and since 

 no notice has been taken of the account I gave of it, and I have reason to be- 

 lieve Mr. Hawksbee lost the table I left with him for the society, of the 

 numbers relating to it, I take this occasion to present the society with the fol- 

 lowing account of it. 



We placed the great loadstone belonging to the Royal Society so, that its 

 two poles lay in the plane of the horizon, and were in a line exactly at right 



