242 rHILOSOPHICAL TRANSACTIONS. [aNNO 16? 5, 



it was found to have only the consistence of dirt, whereas the other had the 

 consistence of slacked lime. The reason of which may perhaps be, that the 

 volatile salts of the lime may exhale while the receiver is exhausting. 



Some plaster of Paris was also slacked in vacuo, and the ebullition of it there 

 appeared much more than in the open air. When it is not touched, the bubbles 

 that issue out leave large holes in it, and then it settles very uneven ; but taking 

 care to stir it till the bubbles escape, and pressing it when it begins to settle, it 

 becomes very smooth, and has fewer little holes than the common plaster. 



An Account given by a French Author, (Denys Papin) in his Booh on the Origin 

 of Fountains, printed 1674, at Paris ; to show that the Rain and Snow-waters 

 are sufficient to make Fountains and Rivers run perpetually. N° 11 9, p. 447. 



In order to give a gross estimate of the quantity of rain,* compared with the 

 quantity of water running away in springs and rivers; it will be first necessary to 

 agree on the way of measuring these two sorts of water. Some persons say, 

 that a cubic inch of water yields, in 24 hours running, 144 muids, (the name 

 of a French measure, holding 280 French pints ;) others say it yields but 70 of 

 that measure. But I have reason to believe that it yields 83 of this measure ; 

 and it is known that a vessel of two feet deep, long and broad, holds one muid 

 of water. 



This being supposed ; it follows, that a vessel which contains 83 muids of 

 water, is able to furnish in 24 hours as much as will make an inch of water run 

 continually. So that, if a conservatory should hold 3378 muids of water, it 

 would furnish for a whole year a sufficient quantity to make an inch of water 

 run constantly. And if it were as large again, it would furnish two running, 

 and so on in proportion. Then for the measure of the rain and snow water ; I 

 have found that from October 1668, to October 1669, there had fallen so 

 much of it, as amounted to the height of 18 inches 7 lines; and from the same 

 month of 1670 to the same month 1671, there had fallen only so much as came 

 to the height of 84- inches ; and from January 1673 to January 1674, to the 

 height of 274- inches. Of which, taking the medium, we have 19 inches and 



* The like to which has been attempted here, and proposed to the Royal Society some years since, 

 by Sir Christopher Wren, who, by the contrivance of a rain-bucket, had taken an account of all the 

 water that fell for a considerable time j and by his weather-clock had, among other particulars, not 

 only taken in the measuring of the quantity of rain that falls, but also the time when it falls, and 

 how much at each time. Which instrument, if put into practice, would be of excellent usej foras- 

 much as it may also serve, by some additions rnade to it by M. Hook, to record tlie weight of the 

 air, the drought, moisture, heat and cold of the weather, the sun-shine, the quarters and strength of 

 the winds : and all this to be performed by only one motion, driving all the parts of tlie instrument^ 

 which is therefore the more considerable, tliat of itself it records its own effects. — Orig. 



