Ste ols Eaticcidd ee 855 
the limit of possible visibility might be extended to zygyoy} 
and as Helmholtz has suggested, this perhaps accounts for Stinde 
having actually been able to obtain a photographic image of 
lines on] Jyooth of an inch apart. It would seem then that, 
owing to the physical characters of light, we can, as Sorby has 
pointed out, scareely hope for any great improvement so far as 
the mere visibility of structure is concerned, though in other 
respects no doubt much may be hoped for. At the same time, 
Dallinger and Royston Pigott have shown that, so far as th 
mere presence of simple objects is concerned, bodies of even 
smaller dimensions can be perceived. 
rby is of opinion that in a length of gyty pth of an inch 
there would probably be from 500 to 2,000 molecules—500, 
for instance, in albumen and 2,000 in water. Even, then, if we 
could construct microscopes far more powerful than any we now 
possess, they would not enable us to obtain by direct vision any 
idea of the ultimate molecules of matter. Sorby calculates that 
defined with our most powerful microscopes would contain 
many millions of molécules of albumen and water, and it follows 
that there may be an almost infinite number of structural char- 
acters in organic tissues, which we can at present foresee no 
mode of examining. 
The Science of Meteorology has made great progress; the 
weather, which was formerly treated as a local phenomenon, 
being now shown to form part of a vast system of mutually 
dependent cyclonic and anti-cyclonic movements. The storm- 
signals issued at our ports are very valuable to sailors, while 
the small weather-maps, for which we are mainly inde ted to 
Francis Galton, and the forecasts, which anyone can obtain on 
application either personally or by telegraph at the Meteoro- 
logical Office, are also of increasing utility. 
Electricity in the year 1831 may be considered to have just 
n ripe for its adaptation to practical purposes; it was but a 
few years previously, in 1819, that Oersted had discovered its : 
; at 
deflective avtion of the current on the magnetic needle, t 
\mpére had laid the foundation of electro-dynamics, that 
Schweizer had devised the electric coil or multiplier, and that 
Sturgeon had constructed the first electro-magnet. It was 
mm 1881 that Faraday, the prince of pure experimentalists, 
announced his discoveries of voltaic induction and magneto- 
had been much advanced by the interesting experiment of Sir 
Charles Wheatstone, proving the velocity of the current in a 
metallic conductor to approach that of the wave of light. 
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