594 ON THE DECENNIAL PERIOD OF MAGNETIC VARIATIONS, ETC. 
aisément dans les cours d’eau, partout ou une cause quelconque diminue ou 
augmente la vitesse des tranches paralleles au sens du mouvement.”* 
66. It is ‘ces causes quelconques” with which we wish to become acquainted. 
The difference of velocities of the photosphere for two different latitudes is con- 
stant, at least I am not aware that it has been found greater in the years of 
maximum spot frequency. What has become then of the causes which disturb 
the equilibrium of contiguous zones in years when there are few or no spots ? 
M. Faye has another hypothesis to explain this. That, on approaching extinc- 
tion, the contraction of the sun due to the external radiation of heat may pro- 
ceed by jerks (saccades), which will produce a sudden increase of heat and 
increased brightness, and that this phenomenon will be repeated till the sun 
becomes extinguished. “ Avant d’arriver a ces oscillations extrémes, les phé- 
noménes beaucoup moins altérés pourront présenter un caractere de périodicité 
réguliére, et telle est, sans doubt, la raison du fait découvert par M. ScHwaBeE et 
mis au pleine lumitre par M. R. Wotr de Zurich.”t It is this hypothesis 
which must be compared with that of planetary actions. M. Faye has said of 
the latter, ‘Ces idées ont cours a l’étranger; elles ont peu de chance d’étre 
acceptées en France.”{ I doubt much that the ideas which the learned French 
academician has substituted will be considered more satisfactory than the 
others. I believe that no hypothesis yet proposed has sufficient weight to be 
accepted generally, and more facts are required before a sure basis for a hypo- 
thesis can be attained. It is hoped that the results of the preceding paper will 
be found to be a contribution to this end. 
* Annuaire du Bureau des Longitudes, 1873, p. 527. * Dbid...1873,.p. 525, 
t Annuaire, 1874, p. 460. 

