VOL. LXV.] PHILOSOPHICAL TKANSACTIONS. 645 



From these circumstances it appears, that water, by being placed in a new 

 situation free from receiving heat from other bodies, and exposed in large sur- 

 faces to the air, may be brought to freeze when the temperature of the atmos- 

 phere is some degrees above the freezing point on the scale of Fahrenheit's ther- 

 mometer ; and by being collected and amassed in a large body, is thus preserved, 

 and rendered fit for freezing other fluids, during the severe heats of the summer 

 season. In effecting which, there is also an established mode of proceeding ; 

 the sherbets, creams, or whatever other fluids are intended to be frozen, are 

 confined in thin silver cups of a conical form, containing about a pint, with their 

 covers well luted on with paste, and placed in a large vessel, filled with ice, salt- 

 petre, and common salt, of the two latter an equal quantity, and a little water 

 to dissolve the ice and combine the whole. This composition presently freezes 

 the contents of the cups to the same consistency of our ice creams, &c. in Eu- 

 rope ; but plain water will become so hard as to require a mallet and knife to 

 break it. On applying the bulb of a thermometer to one of these pieces of ice, 

 thus frozen, the quicksilver has been known to sink 2 or 3 degrees below the 

 freezing point ; so that from an atmosphere apparently not cold enough to pro- 

 duce natural ice, ice shall be formed, collected, and a cold accumulated, that 

 shall cause the quicksilver to fall even below the freezing point. 



XXI IT, Of the Bouse- Swallow, Swift, and Sand- Martin. By the Rev. Gilbert 



fVhite. p. 258. 

 This excellent paper is reprinted in Mr. White's History of Selbome, to which 



the reader is referred. 



'■- ;i . .li/i ( -|Wi!). i 



XXIV. Of a Machine for raising Water, executed at Oulton, in Cheshire, in 

 1772. By Mr. John M'hitehurst. p. 277. 

 Presuming the mode of raising water by its momentum may be new and 

 useful to many individuals, Mr. W. was induced to send a description of a work, 

 executed in 1772, at Oulton, Cheshire, the seat of Philip Egerton, Esq. for the 

 service of a brewhouse and other offices, which was found to answer effectually. 

 The circumstances attending this water- work require a particular attention, and 

 are as follow, a, in fig. 10, pi. 12, represents the spring or original reservoir, 

 its upper surface coinciding with the horizontal line bc, and with the bottom of 

 the reservoir k. d the main pipe, 1-i- inch diameter, and nearly 200 yards in 

 length. E a branch pipe, of the same diameter, for the service of the kitchen 

 offices, situated at least 1 8 or 20 feet below the surface of the reservoir a ; and 

 the cock p was about 16 feet below it. g represents a valve-box, g the valve, 

 H an air vessel, 00 the ends of the main pipe inserted into h, and bending down- 

 wards, to prevent the air from being driven out when the water is forced into it ; 



