Intelligence and Miscellaneous Articles. 157 



Browning, Yogel, and others, a scale could be very easily connected 

 with this instrument, it can be recommended even without one for 

 systematic mass-observations of fixed-star spectra, in which the 

 prime object is to ascertain the typical constitution of the spectra. 

 As the essential differences between these types probably depends 

 only on the temperature and mass of those incandescent bodies, and 

 according to the observations of Secchi and others those types stand 

 in a certain relation to the distribution of the stars in space, such 

 systematically conducted mass-observations may in future become 

 of high importance for the progress of astrophysics. 



I permit myself, in conclusion, the remark that the combination 

 above described was explained and exhibited by me at the last meet- 

 ing of the Astronomical Society at Hamburg, in September 1873. — 

 Berichte der Icon, sacks. GesellscJinft der Wissenschaften matli.-phys. 

 Classe, April 23, 1874. 



NOTE ON THE CAUSE OF TIDES. BY E. J. CHAPMAN, PH.D., PRO- 

 FESSOR OF MINERALOGY AND GEOLOGY IN UNIVERSITY COL- 

 LEGE, TORONTO*. 



The phenomenon of the tides, stated broadly, consists of a pass- 

 ing elevation, real or apparent, of oceanic waters at two opposite 

 points on the surface of the globe. These elevations, w T hich follow 

 the moon in its course, may become greatly intensified under local 

 conditions, as where opposing coast-lines impede the progress of 

 the tidal wave ; but in the open ocean, it is well known, they are 

 of but slight significance. According to the received theory, they 

 are occasioned essentially by the unequal degree of attraction ex- 

 erted by the moon on different parts of the earth — this attraction 

 being, of course, modified by that of the sun. It is thus assumed 

 that the waters, owing to their comparative mobility, are drawn 

 towards the moon on one side of the globe, whilst the solid earth 

 is drawn away from the waters on the other side — or, to use the 

 common phraseology, is drawn towards the moon faster than the 

 waters can follow. 



This view, although not without opponents, has been almost uni- 

 versally adopted in default of a more satisfactory explanation. 



The explanation of the cause of tides now suggested has at least 

 this merit : it applies the same principle in elucidation of both tides 

 — that nearest the moon, and that on the opposite side of the globe. 

 It is briefly this : — When two bodies pull against each other, there 

 must necessarily be a contraction of particles towards the centre of 

 each body along the line of pull or resistance. In the pull, there- 

 fore, of the earth upon the moon, the earth (and of course the moon 

 also) must suffer a passing contraction, the part along the line of 

 pull, so to say, contracting more than the other parts. But this 

 contraction is mechanical only, and is therefore a compression : and 



* Communicated by the Author. Condensed from a communication 

 made to the Canadian institute, February 7, 1874, 



