136 THE ROYAL SOCIETY OF CANADA 



alteration of this formula to suit our particular readings is a simple 

 matter. 



Let V =the velocity in miles per hour^; 



r =the reading in cms. of the gasolene on one side of 

 the tube, i.e. the distance from the scale zero; 

 (thus the "head" = 2 r). 

 d =the density of the gasolene in grams per cc; 

 g = the gravitational acceleration constant in cms. per 



sec. per sec; 

 A =the angle of slope of the stand in degrees; 

 p = the density of the air in grams per cc. ; 



then substituting in the above formula and multiplying by the re- 

 quired constants in order to express v in mis/hr., we get 



r d g sin A 



V = 0-00200 ^ 



P 



In our case d = 0-75 gms/cc, g = 980 cms/sec^, sin A=l-32, and 



p = 0-00129 gms/cc. hence the formula reduced to 



v2 = 151 r 



In the same way formulae could be deduced for any particular slopes 



and densities. 



The two tubes were compared in a fluctuating wind, and the 

 tops of the corresponding liquid columns in each tube were found to 

 keep very closely in line. Occasionally the free period of vibration 

 of the gasoline afïected the readings momentarily by as much as 1 cm. 

 but this was infrequent and was apparently quickly damped. It 

 was thought that damping devices could readily be introduced, which 

 would eliminate this entirely. 



It was somewhat difficult to get the average Pitot reading during 

 half a minute as there was a certain amount of gustiness and the 

 movements of the gasoline were sometimes momentarily erratic and 

 rapid. As the gusts were approximately periodic the following method 

 was adopted. The maximum and minimum readings during the 

 half minute were recorded and their mean taken, also the mean pos- 

 ition of the liquid was estimated by another observer, and the mean 

 of the two results was taken as representing approximately the average 

 reading. It might be suggested that the square of the mean of the 

 square roots should be taken in the first method since the velocity is 

 proportional to the square roots of the readings, and that this would 

 lower the means appreciably. It was, however, found that for the 



^"Miles per hour" was considered more convenient than "metres per sec." 

 because the accuracy of the results was of the order of 1 mi /hr, and these units were 

 also more convenient in other parts of the investigation. 



