296 Transactions— Miscellaneous. 
10. I may state here that I entirely accept that result so far as it goes, 
viz., as establishing the rule that, the cups once fairly under way, the 
centres will travel at about one-third the wind’s velocity, so long as a steady 
rate of speed is maintained, but no longer. 
11. It will be perceived that this last qualification implies a most serious 
possibility of error, inasmuch as the wind’s velocity varies almost every 
moment; however, I am inclined to believe that a really good anemometer 
will give a very fair mean velocity for a lengthened period, such as 12 or 24 
hours, or in other words that it will indicate with tolerable faithfulness the 
total horizontal movement of the air during such periods. This, although 
not fulfilling the first of our two postulated anemometrical desiderata, as 
will be shown shortly, would suffice for the second, viz., comparison of the 
average wind-foree experienced in various localities, provided the anemo- 
metrical records be themselves intercomparable. Let us now examine 
whether this be the case. 
12. In the year 1871, I made a series of experiments at the Southland 
Observatory, with the view of ascertaining whether three of Dr. Robinson's 
anemometers gave approximately identical results, in order that, should this 
prove to be the ease, I might place them in as many different localities to 
obtain comparative records of wind-foree. Of these instruments two were 
the ordinary double-indexed single-dial anemometers by Casella, with cups 
three inches in diameter, and registering to 505 miles, and the third was 
an improved five-dial instrument by Negretti and Zambra, with cups four 
inches in diameter, and registering to 1,000 miles. A single week's trial 
sufficed to prove all comparison hopeless. The three instruments were 
exposed in a precisely similar way, and their individual positions were 
interchanged. Nevertheless, their records varied so widely as to be simply 
ridiculous and unworthy of preservation; accordingly, I relinquished my 
plan of comparing the respective local wind-forces, and adopted the Negretti 
anemometer, being apparently the most trustworthy, as my standard. As 
an instance of the variety in the records of these three instruments, I may 
mention that in one of my 24 hours’ observations, when the Negretti 
anemometer indicated 517 miles, one of the Casella instruments indicated 
370, and the other 283 miles. So much for my own personal experience. 
13. About the same time, similar but more elaborate experiments were 
being carried on in England, on behalf of the Meteorological Society, by Mr. 
Fenwick Stowe, and by Mr. Robert Scott, the Director of the Meteorological 
Office. Both have published the results. Mr. Stowe’s were the most ex- 
tended observations, and I extract the main conclusions at which he arrived. 
No fewer than ten anemometers were thus tested, Nos. 1, 2, and 8 being 
the same as in my experiment; No, 4, one by Adie, with four-inch brass 
