APPENDIX D . LXXXVII 



of the sun. The mirrors and mechanism for the telescope and spectro- 

 scope are, however, all ready to be moimted as soon as the building is 

 ready. Photographs of the sun's surface on a fecale of about 7^ inches to 

 the sun's diameter are taken on every cloudless day, to serve as a record 

 of sun spots. Research on the sun will be considerably extended as soon 

 as the ccelostat house is completed by spectrograms of isolated portions of 

 the surface such as spots, by a spectroscopic determination of the solar 

 rotation, and by numerous allied investigations. 



Geophysics. 



Seismology. — During the past year the two Bosch photographic 

 horizontal pendulums have been in constant operation, and have been ver)' 

 satisfactory. The time scale is 90 cm. per hour. The records as given by 

 the seismograms are classified as macroseisms and microseisms ; the 

 former represent earthquakes, as the word is generally understood, while 

 the latter represent minute pulsations of the crust of the earth. While 

 the cause of the former is believed to reside in the lithosphère and hydro- 

 sphere, that of the latter appears to be related more closely to the atmos- 

 phere. During the past year Canada joined the International Seismo- 

 logical Association, and thereby the Observatory has been brought in 

 touch with all the important earthquake stations of the world. This 

 enables comparisons to be made of various seismograms of the same 

 phenomenon, and affords means for a study of the velocity of propaga- 

 tion of the various forms of earthquake Avaves, involving the relative 

 elasticity and density- of the media through which they pass. Compari- 

 sons made here during the past year show that the longitudinal waves 

 which give the first preliminary tremors of an earthquake travel with 

 a velocity dependent upon the depth of their path, but reach a maximum 

 velocity at a depth of about IGOO kilometres, w^here it is about 11 km. 

 per second, say 410 miles per minute, while the lower limit lies between 

 7 and 8 km. per second. Similarly for the slower, transverse waves, the 

 velocity rises from 4.5 to nearly 7 km. per second at the above depth, 

 while the surface waves have an average velocity of 3.4 km. per second. 

 Having now a fairly accurate knowledge of the speed of propagation of 

 the variou^ kinds of waves, a single seismogram, where it is possible to 

 recognize the various phases of the waves, will give readily the distance 

 to the epicentre or disturbed area, within about 60 miles. The record 

 of earthquakes is communicated to the Press together with the estimated 

 distance and probable location. 



The microseisms have received considerable attention. They are 

 studied by comparison with the daily barograms and with the isobars 

 and gradients of the dailv weather charts of Canada and the United 



