240 Mr. W. H. Dines. [June 19, 



1 foot from its axis of rotation, and when corrected as far as possible 

 for all sources of error, is given as 100, the values of all other 

 moments being expressed relatively to it. 



The actual value in terms of the velocity is given subsequently. 



Square Pressure Plate. 



Curves A and B show the relation between the angle of incidence 

 and the moments for positions I and II, as deduced from the first un- 

 corrected series of experiments, and curves E and F for positions III 

 and IV (figs. 8 and 9). In taking the values of these moments there 



Fia. 8. Diagram of Moments. Square Plate. 



is one point of which we must not lose sight. The long arm of the 

 whirling machine is not perfectly rigid, and gives way under the 

 torsion produced by the wind pressure. Experiments made by 

 hanging weights from the end of a lever showed that a force of 5 Ibs. 

 acting 1 foot from the axis caused a deflexion of 2, and since this is- 

 about the moment caused by a velocity of 40 miles an hour, when the 

 plate is exposed normally, the curves have been drawn on the suppo- 

 sition that a moment represented by 100 caused a deflexion of 2, and 

 that the other moments caused a proportionate deflexion. 



It was on this account that it was found advisable to make all the 

 experiments at one uniform velocity. 



