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XXIII. On the Determination of the Constants of the Cup Anemometer by Experiments 
with a Whirling Machine. 
By T. Eh Robinson, D.D., F.R.S., &c. 
Received March 14 — Read April 4, 1878. 
[Plates 66-70.] 
In a communication to the Royal Irish Academy (Proceedings of the Royal Irish 
Academy, December, 1875), in which I examined the experiments made by M. 
Dohrandt to determine the constants of the cup anemometer by means of Robins’ 
whirling machine, I expressed a hope that I might have an opportunity of making 
similar experiments free from some influence which seemed to me objectionable. 
This opportunity was soon afforded me by a liberal grant from the Donation Fund 
of the Royal Society. I lost no time in having the necessary apparatus constructed 
by Mr. Howard Grubb, of Dublin, and I now propose to give the results which 
I have obtained with it. 
(1.) I was at first embarrassed by the difficulty of finding a suitable locality for the 
machine. In the St. Petersburg experiments the anemometers passed in their rotation 
at unequal distances from the walls of the building, and were too near its roof, which 
seemed likely to introduce extra disturbances into the air vortex which is formed by 
the whirl of the machine, and which, as will be seen, is a notable element of uncer- 
tainty in these investigations. But this was removed by Mr. H. Grubb placing at 
my disposal the central dome of his works at Rathmines, then recently constructed 
for mounting the great equatorial which he is making for the Vienna Observatory. Its 
basis is a regular dodecagon, 42 feet least diameter, and 42 feet from its floor to the 
summit of the dome. Round it, at 10 feet from the ground, runs a gallery 2 feet 
wide, with a light iron railing, from which several doors give access to workshops 
in which polishing and other light work is executed. On the ground, open arches 
communicate with shops, in which large lathes and other heavv tools are established. 
Tins seemed all that I coidd wish, but, unfortunately, I could have the use of it only 
till the end of June, when it was wanted for the erection of the equatorial. There 
were, however, two inconveniences to be feared. One was that the open arches might 
admit irregular currents of air ; the other was that when heavy turning or planing 
was going on, tremors were produced in the ground which might be expected to make 
the friction of the apparatus vary. I supposed, however, that this disturbance w r ould 
equally affect the motion of the anemometers and the measures of their frictions ; but 
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