PHENOMENA OF THE ZODIACAL LIGHT. 501 
emanation, or an enlargement of its dimensions; and whether this be any con- 
comitant symptom with the appearance of spots on the sun, or magnetical dis- 
turbances on the earth,—are matters still to be determined by observation. 
The physical constitution of the zodiacal light seems also well worthy of being 
inquired into. The most probable supposition is, that which makes it consist of 
innumerable small planetary particles revolving about the sun, and shining. by 
reflected, or not impossibly by direct light. Not impossibly, because while, on 
the one hand, the occasional crossing of the earth’s orbit by the extremer portions 
of the zodiacal light, has been by many held to be the origin of the shooting stars ; 
and many of them have been found to be, at the time of their incandescence, 
several hundred miles above the earth’s surface, and thus far above the limits of 
the atmosphere, whose friction might have imparted such a degree of heat to a 
body at a lower altitude, moving with a velocity of 1000 miles per minute ;—on 
the other hand, M. Maruieson has recently made some most interesting experi- 
ments, in which the thermomultiplier shewed evident indications of radiant, and 
therefore direct heat, proceeding from the zodiacal light.* 
But in its present stage, the subject can only be profitably and successfully 
prosecuted in other climates, in countries where the twilight is shorter, where the 
ecliptic makes, all through the year, a larger angle with the horizon than here. 
and where there are clearer skies, and a more transparent atmosphere. 
As such conditions are well commanded by some of the magnetical and me- 
teorological observatories which have been lately established on a similar foot- 
ing to that of Makerstoun, in connection with the Royal Society of Edinburgh; 
and as the species of phenomenon is one that belongs eminently to those de- 
partments,—we might expect ere long to enjoy much more intimate and exact 
knowledge of the laws and relations of this wondrous and extensive member of 
the solar system, if the Royal Society were to give its testimony that the pheno- 
menon was one of a nature worthy of scientific investigation; as well as that all 
_ that has been done hitherto is insufficient, except for mere approximative pur- 
poses, and has been labouring under geographical disadvantages, which need not 
by any means continue to shackle observation in the present day. 
* Comptes Rendus, t. xvi., p. 687; Ap. 1843. 
VOL. XX. PART III. 6T 

