646 . PHILOSOPHICAL TRANSACTIONS. [aNNO 1775. 



w the surface of the water. Now it is well known, that water discharged from 

 an aperture, under a pressure of l6 feet perpendicular height, moves at the rate 

 of 32 feet in a second of time ; therefore such will be the velocity of the water 

 from the cock f. And though the aperture of the cock p is not equal to the 

 diameter of the pipe d, yet the velocity of the water contained in it will be very- 

 considerable : consequently, when a column of water, 200 yards in length, is 

 thus put into motion, and suddenly stopped by the cock f, its momentous 

 force will open the valve g, and condense the air in h, as often as water is drawn 

 from F. In what degree the air is thus condensed, is needless to say in the in- 

 stance before us ; therefore Mr. W. only observes, that it was sufficiently con- 

 densed to force out the water into the reservoir k, and even to burst the vessel 

 H, in a few months after it was first constructed, though apparently very firm, 

 being made of sheet lead, about 9 or 10 pounds weight to a square foot. 

 Whence it seems reasonable to infer, that the momentous force is much superior 

 to the simple pressure of the column ik ; and therefore equal to a greater resist- 

 ance, if required, than a pressure of 4 or 5 feet perpendicular height. It 

 seems necessary further to observe, that the consumption of water in the 

 kitchen offices is very considerable ; that is, that water is frequently drawing 

 from morning till night all the days of the year. 



XXV. On Occullations of Stars and Geometrical Theorems. Being an Extract 

 of a Letter from Mr. Lexel, to Dr. Morton. Dated Petersburg, June 14, 

 1774. p. 280. 



As I propose, says Mr. L., to make some researches concerning the difference 

 of the meridians of the principal Observatories of Europe, which I am per- 

 suaded can best be ascertained by the occullations of the fixed stars by the moon ; 

 it would be of great service to me to be furnished with the observations that 

 have been made, or that will be made, this year, of the occullations of a, or of 

 y Tauri by the moon. I beg therefore Sir, you will please to desire Mr. Mas- 

 kelyne to communicate them to me, towards the beginning of the next year, 

 directed to Mr. Euler, secretary of our Academy. It would also be of great 

 use to me to have the observation of the occultation of the Pleiades by the 

 moon the 15th of March, 1766, in case it has been taken at Greenwich. The 

 following are some observations of Mr. Wargenlin, of the occullations of 

 « and y Tauri. 



. Emersion of «, uncertain to some seconds. 

 . Immersion of the eye of rt , 1 , ,, 

 .Emersion, ' "' j both very certain. 



. Immersion of y, very certain. 

 . Emersion, within 2 seconds. 



