Direction of the Wind, JSfeio Haven, Conn. 



293 



Mr. Glaisher, who has charge of the Meteorological Department of 

 the Greenwich Observatory, to select an anenionieter similar to one 

 of those in nse at Greenwich, to set it up in proper position and 

 observe it carefully for a sufficient time to determine its error as 

 compared with the Greenwich instruments. Mr. Glaisher promptly 

 acceded to this request, and selected a Robinson anemometer made 

 by Negretti & Zambra of London. The diameter of the cups was 3"8 

 inches, the distance between the centers of the opposite cups was 13 "8 

 inches, and the instrument recorded the wind's progress up to one 

 thousand miles. From a comparison continued for several weeks Mr. 

 Glaisher concluded that the readings of this instrument needed to be 

 increased in the ratio of 93 to 100, in order to make them accord 

 with the Greenwich standards. This anemometer was received in 

 New Haven in the winter of 1867, and was immediately set up on 

 the same tower as the former instrument, and distant fi-om it sixteen 

 feet. Both instruments have been observed regularly to the present 

 time, the observations having been made chiefly by Prof. E. Loomis. 

 It is found that the results obtained from the two instruments differ 

 but slightly. When the velocity of the wind is small, the Negretti 

 anemometer gains somewhat upon Casella ; and when the velocity is 

 great, Casella gains somewhat upon Negretti ; but in the results of 

 an entire year, the difference between the two instruments is entirely 

 inappreciable. 



Table V contains a summary of the distances traveled by the wind 

 for each month since the observations commenced, according to the 

 indications of each anemometer. In column 3rd are given the 

 dates of the observations corresponding most nearly to the beginning 

 and end of each month ; column 4th shows the included interval of 

 time expressed in hours ; column 5th shows the distance traveled by 

 the wind during the preceding interval accoi'ding to Casella's ane- 

 mometer, and column 6th shows the distance for the same interval 

 according to Negretti's anemometer ; columns 7th and 8th show the 

 mean hourly velocity deduced from the observations with the separate 

 instruments. The following table affords a comparison of the indica- 

 tions of the two instruments, the velocities given for the Casella 

 anemometer being the mean velocities determined for the years of 

 observation when both instruments were employed. 



Comparison of CasellaCs and Negretti's Anemometers. 



2lA 



