SCIENTIFIC SFMMAKY. 
219 
coil, tlie act of exciting the coil will charge and discharge it at once ; as the 
size of the jar is diminished, it will he charged and discharged oftener, and 
the anreol will begin to mingle itself with the spark discharges, and as the 
size still further diminishes, will finally replace all of them except the firsts 
I for it is evident that we may regard two brass balls, with an intervening 
layer of air a millimeter thick, as a minute Leyden jar, representing the last 
of the series. 
The Spectrum of Lightning has been recently obtained by Lieutenant E. 
S. Holden. (S. A. J. Dec.) He says that from the sheet lightning he 
repeatedly obtained series of bright bands in the green, but the width and 
intensity *of these bright bands continually changed. Of the bright and 
j sharp lines he saw but three : — 1, line in green ; 2, line in blue ; 3, line in 
i violet (or extreme blue?). These were seen frequently, and sometimes 
those of one flash would be immediately succeeded by those of the follow- 
I ing flash, thus giving him a means of assuring himself that the same lines 
i appeared as well in position as in colour. The second set he regards as 
' trustworthy. The observations were taken at West Point, N. Y., August 
22nd, 1872, at 6 ‘00 p.m., looking toward the east through a violent rain. 
The spectroscope was first directed toward the sky, and the spectrum with 
dark lines, which was constantly seen, was mapped as below, and the follow- 
, ing notes taken : 
1 
Green. Bed. 
7 6 5 4 3 2 1 
Notes — The red ends slightly 
beyond 1. 
2 = D line. 
3 bounds yellow hne. 
5 near boundary of green. 
6 seems to be sometimes green 
and sometimes blue. 
7 violet = H. 
The spectroscope was then turned to the lightning, and with the above 
I dark lines as reference lines the following bright lines were mapped : {a) 
bright line less refrangible than red end (border) of spectrum, i. e., extra red ; 
(&) bright line slightly more refrangible than 4 j (c) bright line near 5 or 6 
; green or blue j ” id) bright line in blue between 6 and 7, once seen, bright 
purple. 
' The Wear of Stone. — ^At a meeting of the Literary and Philosophical 
; Society of Manchester ” (too late for the last number of this Journal) Dr. 
A. Smith said that he, like others, had observed that the particles of stone 
I most liable to be in long contact with rain from town atmospheres, in 
England at least, were most subject to decay. Believing the acid to be 
the cause, he supposed that the endurance of a siliceous stone might be 
somewhat measured by measuring its resistance to acids. He proposed 
therefore to use stronger solutions, and thus to approach to the action of 
j long periods of time. He tried a few specimens in this way, and with most 
i promising results. Pieces of about an inch cube were broken by the fall of a 
; hammer, and the number of blows counted. Similar pieces were steeped 
, in weak acid ; both sulphuric and muriatic acids were tried, and the latter 
I preferred. The number of blows now necessary was counted. Some sand- 
stones gave way at once and crumbled into sand j some resisted long. Some 
very dense siliceous stone was little affected j it had stood on a bridge 
unaltered for centuries — in a country place, however. These trials were 
