192 REPORT—1840. 
1. That Turbines are with equal advantage applicable for high and for 
low falls. 2. That their net useful effect equals 70 to 78 per cent. of 
the theoretical effect of the power. 3. That they may work at speeds 
varying from 
where x = number of revolutions ; V = velocity due to fall; R = ex- 
treme radius; the useful effect still not differing notably from the 
maximum. +4. That they work at very considerable depths under 
water, the relation of useful to theoretical effect not being thereby 
much diminished. 
On producing True Planes or Surfaces on Metals. 
By Mr. JoserpH WuitworTu. 
Surface plates were exhibited, of which, if one be put upon the 
other, it will float, until by its weight it has excluded some of the air, 
when the two will adhere together with considerable force. These 
surfaces were got up without grinding. The only operations performed 
upon them were those of planing, filing, and scraping. Practically, 
the excellence of a surface consists in the number and equal distribu- 
tion of the bearing points. But if a ground surface be carefully 
examined, the bearing points will be generally found lying together in 
irregular masses, with extensive cavities intervening. The cause of 
this irregularity is in the unmanageable nature of the process. The 
action of the grinding powder is under no control. There are no 
means for securing its equal diffusion, or for modifying its application, 
with reference to the particular condition of different parts of the sur- 
face ; the practical result is, that the mechanic neglects the proper use 
of the file, knowing that grinding will follow, to efface all evidence 
either of care or neglect. In various departments of the arts and 
manufactures, the want of improvement in this respect is already felt. 
The valves of steam-engines, for example, the tables of printing presses, 
stereotype plates, slides of all kinds, require a degree of truth much 
superior to that they now possess, for want of which there is great 
waste in time, in steam power, in wear and tear, and, above all, in skill 
misapplied. The improvements so much to be desired will follow upon 
the discontinuance of grinding. The surface plate and the scraping 
tool will then come into use, and a new field will be opened to the 
skill of the mechanic. Supposing him to be provided with a true 
surface plate, he will find no difficulty, after a little practice, in bring- 
ing up his work to the required nicety. For this purpose he will find 
it advantageous to employ a scraping tool made from a three-sided file, 
and carefully sharpened on a Turkey stone, the use of which must be 
frequently repeated. A light colouring matter, such as red chalk and 
oil, being spread over the surface plate, and the work in hand applied 
thereto, friction will cause the prominent places to be marked, which 
will instruct the experienced mechanic where and how to operate to 
the greatest advantage. 
