520 Prof. J. C. McLennan on the Relative Intensities of 



of a string under the same conditions. They represent the 

 1st and 5th types together in one plane and the 2nd by itself 

 in the perpendicular plane. In fig. 12, the 1st and 5th types 

 are in the same phase, and in fig. 13 they are opposed. 

 Figs. 14 and 15 show the 1st type in one plane, and the 

 2nd and 6th types together in the perpendicular plane. 

 The two latter are in different relative phases in the two 

 photographs. 



Regarding the plate as a whole, it is not a little surprising 

 to contemplate that a strictly normal motion imparted to one 

 extremity of a stretched string should result (under suitable 

 circumstances) in such an extraordinary variety of types of 

 oscillation ! I do not think I have photographed one-half 

 of the different types that can easily be maintained 

 permanently. 



Conclusion : — I have indicated some of the principal results 

 of experimental interest obtained with this class of maintained 

 vibrations. Further experimental work on the leading types 

 and a detailed comparison with the results of the physical 

 theory which 1 have outlined above and with the mathe- 

 matical analysis, does not fall within the limits of the present 

 paper, and I hope to deal with them on an early date. Mean 

 while I must remark that the existence and physical import- 

 ance of the small " second " term of lower frequency in the 

 expression for the maintained motion is directly demon- 

 strable by stroboscopic observation of each of the five or six 

 types of maintained motion referred to above and by a study 

 of their "vibration-curves." The results of this work are 

 being prepared for publication. The experiments and obser- 

 vations recorded in this note were made at the Physical 

 Laboratory of the Indian Association for the Cultivation of 

 Science, Calcutta. 



!XLIX, On the Relative Intensities of the Earth's Pene- 

 trating Radiation on land and Sea. By Professor J. C. 



McLennan, University of Toronto *. 



I. Introduction. 



SINCE the discovery of the existence of a penetrating 

 radiation at the surface of the earth in 1902 f , numerous 

 measurements of its intensity have been made in different 



* Communicated by the Author. Read before the Eoyal Society 

 of Canada, May 17, 1912. 



t McLennan & Burton, Phil. Mag. v. 1C03; Coolve, Phil. Mag. vi. 

 1903. 



