[ 37 2 ] 
XXXV. A Memoir concerning the mofi 
Wheels , etc. by Mr. Mallet of Geneva.. 
Communicated by M. Maty, M. D. Sec . 
R. S. Tranjlated from the French, by 
J. Bevis, M. D. R. S. S . Read March 
26, 1767. 
§ I.f" i t H E Stream of rivers is of fueh im- 
portance in moving machines of all 
kinds, that any attempt towards perfecting this part 
of mechanics may be confidered as of very- great 
utility. 
The firft wheel on which the Stream aCts is one of 
the molt eSfential members of the machine, and it is 
ealy to difeern that the greater or lefs effeCt thereof 
mull depend, in a great meafure, on the manner of 
constructing this wheel, and on the dimensions 
given to it. I Shall not at prefent inquire whether 
wheels of different constructions from thofe which 
have been long in ufe might be advantageoufly Sub- 
stituted in their Stead ; but confine myfelf, in this 
effay, to an examination of the moft common ones, 
and to discover the means by which they may be 
made to produce the greatest poShble effects. Their 
construction is very Simple ; they confiSt of feveral 
planes inferted into the fame axle placed horizontally 
above the furface of the water, and in a polition 
perpendicular to the Stream. Thefe planes, called 
