780 
DR. T. R. ROBINSON ON THE DETERMINATION OF 
others, so that the rope after leaving them and crossing, goes round the driving pulley 
on the vertical shaft. On the axle of D is fixed a large drum, E, which gives motion 
to it, being driven by a band from a Porter’s wheel. These pulleys are 15 inches 
diameter, and their spindles -fths of an inch. To G and H weights of 60 lb. are hung to 
maintain the requisite tension on the driving pulleys. If an additional weight, D, be 
hung to G, and the drum turned so as to raise it, it is obvious that when G descends 
the rope C I will be drawn up, F K drawn down, and H up ; therefore the vertical 
shaft will be turned with a uniform speed by a force half D (neglecting friction) as 
long as G remains suspended. It works freely. When the anemometer was removed 
from the end of the horizontal arm, V=52 miles with D = 20 lb. I made, however, a 
great mistake here, from motives of economy, in using manual labour as the motor of 
this apparatus, instead of adopting the suggestion of Mr. Grubb of constructing an 
additional piece, by which the power of his steam engine could have been applied to 
drive it with any required speed. It would have been far less expensive than the 
labour proved to be ; and I could have carried my experiments to a far higher 
velocity. When D exceeded 30 IE., two men were required at the wheel ; and in 
one instance, where it was 105 lb., four men were required, and with difficulty could 
go beyond three minutes of the exertion. 
(7.) Opposite the driving frame is a platform which gives easy access to the anemo- 
meter for measuring its friction, and cleaning or oiling the various bearings. It is a 
trapezium 10 feet long, the longer end of which is 8 feet long and is hinged to the 
platform of the gallery ; the shorter end, which is 2 feet long, reaches towards the 
anemometer. When in use it is supported by a strut resting on the ground ; at other 
times it hangs vertically, and its influence to disturb the air vortex, was found to be 
insensible. 
(8.) Five anemometers were experimented on. No. I. is of the Kew type : its cups 
9 inches diameter, its arms 24 inches long ; but instead of being of thin plates moving 
edgewise, it was necessary to make them of steel tube 0'5 inch external diameter, as 
stays could not be applied to oppose the centrifugal force, and even these were scarcely 
strong enough.* Its weight = 110'87 oz. In No. II. the cups are 4 inches diameter, 
and the arms 24 inches; the weight = 7 2'5 oz. No. III. has cups 9 inches and arms 
12 inches; weight =68 '25 oz. No. IY. has cups 4 inches and arms 12 inches ; weight 
= 40 '5 oz. No. Y. was tried as a matter of curiosity; its cups were semicylinders 
with mouths 9 inches square, the planes which closed their ends set parallel to the 
* The equation (C) given when treating of centrifugal friction enables us to compute the outward 
throw due to this cause. One of the 9-inch cups weighs 12 oz., and its arm 15' 7 oz. At the highest 
V which I obtained with them = 36'29 miles this throw =124'8 oz. acting at their C G by a leverage 
= 17 2 Now we found that 80 oz. acting on the arm by leverage =19'5 inches deflected the centres of 
the cups outwards 0'275 inch. This would make the real V in this case 0'091 mile greater than the 
estimated one. I did not, however, think it necessary to take this into account, as there are so many 
other and more important cases of uncertainty. 
