AN IMPROVEMENT IN ANEMOMETERS. 

 By H. C. Russell, B.A., F.R.S. 



[Bead before the Royal Society of N.S.W., July 4, 1888.] 



One ot the most interesting and practically important questions 

 in relation to wind, is what is its maximum velocity or pressure, 

 for the one depends on the other. I need hardly say that 'many 

 attempts have been made to devise instruments capable of 

 answering that question. It has been generally admitted that 

 existing Anemometers using Robinson's Cup are unequal to the 

 task, because a gust lasts but a few seconds, often not more than 

 five or six, and the recording parts made to register an hour's 

 work on \ an inch or 1 inch of paper will not shew satisfactorily 

 a gust lasting 10 seconds, that is j^q part of an hour ; or, in other 

 words, if one could measure such a gust, it would be 3~6 o part of 

 an inch on the paper, and the smallest error in measuring becomes 

 so magnified when the measured velocity in 10 seconds is converted 

 into velocity per hour, that results are rendered very uncertain. 

 Pressure plates have also been tried in every form, but it is found 

 the results are not satisfactory, because when a gust of wind 

 coming along at a velocity of say 50 miles an hour strikes a 

 pressure plate, it has just the same effect upon it as if it were a 

 hammer striking it a blow : it sets it into rapid motion which by 

 acquired momentum carries it much further than it ought to do. 

 Now Robinson's Cups are free from this defect, and although not 

 without drawbacks, they are in my opinion the best means we 

 have of recording gusts of wind. Of course the open cup, like 

 the pressure plate, is struck by the advancing gust, but at the 

 same moment the same gust strikes the back of the opposite cup 

 and resists any tendency to run away, and it seemed to me that 

 what was wanted was a means of recording with all possible 

 accuracy, the interval of time which the cups took to run a given 

 number of evolutions, and I have accomplished this by putting in 

 a series of pins in the first wheel, so that they make an electrical 

 contact on a light gold spring for every 10 revolutions of the cups. 

 So far there is nothing new. Many Anemometers have been 

 made to record by electrical contacts. The point that I think 

 is new, is that these contacts are recorded on either of the 

 astronomical chronographs, so that the interval between two 

 contacts can be determined with certainty to within one-tenth of 

 a second or even less. The intention is to use this method only 



