306 Notices respecting New Books. 



The above description may be found useful to some who are de- 

 sirous of making projections of the solar spots. Sir John states that 

 he did not consider it worth while to engrave and publish all the 

 drawings made by him, but he gives a list of the days on which they 

 were made, " in case it should ever be considered necessary to appeal 

 to any of them as records of the state of the sun's surface at that 

 time ;" and he observes, it is much to be wished that all who habi- 

 tually make such drawings would at least place the days for which 

 they possess them on record, in order that it may be rendered possible 

 to ascertain the state of the sun by actual observation on any given 

 day. 



After giving some further particulars respecting the mode of deli- 

 neating the spots, he calls attention to the following points shown 

 by the drawings as characteristic or remarkable: — 1st, to certain 

 forms frequently reproduced on the sun's surface ; 2ndly, to the 

 remarkable radiated or striated apparent structure of the penumbra 

 in certain cases ; 3rdly, to the total absence of all penumbra in some 

 spots ; 4thly, to the occurrence of distinct shades in certain parts of 

 some penumbra ; and lastly, to the immense area occupied by some 

 of the spots with their penumbra; represented in the drawings. As 

 instances of enormous magnitude, he mentions that the spot observed 

 on March 29 occupies an area of nearly five square minutes ; and as 

 a square minute on the sun corresponds to 756,000,000 square miles, 

 '* we have here an area of 3,780,000,000 square miles included in 

 one vast region of disturbance, and this requires to be increased for 

 the effect of foreshortening. The black spot of May 25 would have 

 allowed the globe of the earth to drop through it, leaving a thousand 

 miles clear of contact on all sides of that tremendous gulph." — P. 432. 



He next proceeds to consider a question which may be regarded 

 as the most interesting which can be proposed in connexion with the 

 subject, namely, " to inquire for an efficient cause — for a vis motrix 

 — to give rise to such enormous dynamical phenomena, for such 

 they undoubtedly are ; " and after remarking that the cause of the 

 movements which we observe must reside within the sun itself, and 

 must be there sought for, he thus continues : — 



" Whatever may be the physical cause of the spots, one thing is 

 certain, that they have an intimate connexion with the rotation of 

 the sun on its axis. The absence of spots in the polar regions of 

 the sun, and their confinement to two Zones extending to about 35° 

 latitude on either side, with an intermediate equatorial belt much 

 more rarely visited by spots, is a fact notorious in their history, and 

 which at once refers their cause to fluid circulations, modified, if not 

 produced, by that rotation, by reasoning of the very same kind 

 whereby we connect our own system of trade and anti-trade winds 

 with the earth's rotation. Having given any exciting cause for the 

 circulation of atmospheric fluids from the poles to the equator, and 

 back again, or vice versd, the effect of rotation will necessarily be 

 to modify those currents as our trade-winds and monsoons are mo- 

 dified, and to dispose all their meteorological phenomena on a great 

 scale which accompany them as their visible manifestations in zones 



