ee a 
4 Lg > 4 
Nov. 17, 1870] 
N 
__ 


NATURE 
51 

Thus, though the practical effect of the lamp only 
extends about 300 metres from its position, the field is 
illuminated to the extent of 700 metres, for the benefit of 
all placed between the light and the object. Thus a 
sentinel on the ramparts can see about 3,000 metres from 
the eceinte, and by this means strict watch is kept upon 
the plains around the city at night, as far, in one direction, 
as 1,000 metres beyond St. Denis. M. Bazin is now occu- 
pied in applying his apparatus to the purposes of night 
telegraphs, by the adoption of the system of flashes—men- 
tioned some time since in the Avgéweery—and with the 
aid of coloured lenses. A corvette—the Co/zgny —already 
possesses such a signal apparatus, and the signals are 
distinctly visible at more than eight miles’ distance. The 
action of the lamp, and also the movements of the appa- 
ratus, are remarkably steady, and M Bazin has received 
high testimonials from the authorities of the good working 
I eS eee ee ee 
il 
aa a 
Ra: date ls 

a oe 
of his instrument. 
M. Viollet-le-Duc, who is M. Alphand’s second in com- 
mand of the corps of civil engineers and architects aiding 
the military authorities, has made an interesting report to 
General Trochu respecting the works executed during the 
past month by the auxiliary engineers around Paris. It 
appears, according to this document, that the expense of 
these works has been only 105,000f., while under the 
military system they would have cost 230,000f. We have 
not seen the report, but we presume that M, Viollet-le- 
Duc, and the other architects and engineers, gave their 
services and advice gratis, and this would, of course, save 
the country a considerable sum. 
The Government has voted the sum of 40,000 francs to 
enable M. Dupuy de Léme to carry out his proposed plan 
of navigable balloons. The subject has been twice dis- 
cussed in the Academy of Sciences, and although some 
members have advocated the use of a small steam-engine 
or other motive power, M. Dupuy de Léme is no doubt wise 
in adhering to manual power, which presents all the force 
necessary with none of the inconveniences of machinery, 
and an adaptability to circumstances which no machinery 
can possibly possess. The men will form a crew to aid 
the landing of the balloon, or in extricating it from any 
difficulty, while any engine would be, when not in use, a 
dead weight and awkward encumbrance. Moreover an 
aérostat, with steam or other power, is now in construc- 
tion by another inventor or adapter. 
During the discussion M. Dupuy de Léme showed by 
calculations that his balloon would have a constant ascen- 
sional force up to 870 metres altitude, but beyond that to 
I,110 metres a little gas must be lost. At all events, be- 
tween 250 metres and 870 metres the altitude could oscil- 
late (by means of the extra pocket or swimming bladder) 
without loss of gas; and, of course, there would be the 
usual expedient of ballast to be depended on also. Dr. 
Monra advocated the use of heated air in place of gas. 
Fifty deg. Centigrade would be sufficient, and the heat 
might be retained by making the balloon double—that is 
to say, one balloon within another. The Aigle Mongol- 
fiére, said the Doctor, used to be inflated in twenty 
minutes, while it takes a whole day to fill a balloon (up- 
wards of 1000 cubic metres) with gas. Mongolfier bal- 
loons sent up within twenty leagues of Paris would 
certainly fall in the city, and it is a pity they have not 
been tried before this. Should the siege not soon be 
raised, will not the English aéronauts or others try and | 
send a few letters into Paris? 

PROFESSOR HELMHOLTZ ON FARADAY 
WE have been favoured by Prof. Tyndall with the 
to the German Edition of “ Faraday as a Discoverer,” 
recently superintended by Professor Helmhol'z :— 
“The name of Faraday is one to be held in reverenc2 
by all natural philosophers. Many times in London, 

following translation of a portion of the preface | 

in connection with lectures which I delivered at the Royal 
Institution, I had myself the privilege of his obliging 
help and the pleasure of his amiable society. The perfect 
simplicity, modesty, and undimmed purity of his cha- 
racter gave to him a fascination which I have never 
experienced in any other man, I had therefore a duty 
of gratitude to fulfil towards him. 
“ But apart from this, and apart from that friendship for 
Faraday’s younger associate and successor, the author 
of this book, which induced me to undertake the task, I 
believed that I should render a service to German readers 
by facilitating, as far as in me lay, an insight into the 
action and character of a mind so richly and peculiarly 
endowed, and so entirely the product of natural growth. 
“Tt is, moreover, by no means for the philosopher only 
that such an insight possesses interest. His interest, 
certainly, is the most immediate, for it has hardly been 
the lot of any single man to make a series of discoveries 
so great and so pregnant with the weightiest consequences 
as those of Faraday. Most of them burst upon the world 
as surprises, the products, apparently, of an inconceivable 
instinct; and Faraday himself, even subsequently, was 
hardly able to describe in clear terms the inteliectual 
combinations which led to them. These discoveries, 
moreover, were all of a kind calculated to influence in the 
profoundest manner our notions of the nature of Force, In 
the presence of Faraday’s magneto-electricand diamagnetic 
discoveries more particularly, it was impossible for the 
old notions of forces acting at a distance to maintain 
themselves, without submitting to essential expansions and 
alterations. The clearer expression of these changes is at 
the present hour the object of physical science. 
“In what way such extraordinary results were achievedis 
naturally a question of the first interest to the investigator 
who strives after similar though more modest ends. But 
Faraday’s development appears to me to possess no small 
human interest in relation to many theoretic questions of 
psychology, and to the art of education. The external 
conditions under which he cultivated those striking 
capacities which excite our wonder were the simplest that 
can be imagined. He was completely self-taught ; brought 
up in humble circumstances, having received no more than 
the commonest instruction, and having been only favoured 
by fortune in the circumstance, that when he was a poor 
apprentice to a bookbinder, he found, at the right time, a 
helper in Humphry Davy, who recognised his peculiar 
gifts, and procured for him the possibility, though in a 
subordinate position, of working in the direction towards 
which his genius impelled him, 
“ And throughout his whole life and labours, the advan- 
tages and disadvantages of such a mode of develop- 
ment reveal themselves in simpler and larger traits 
than in the case of most other similar celebrated names. 
The principal advantage rose undoubtedly from the fact 
that his intellect was not too soon subjected to theoretic 
fetters, but enjoyed its freedom in the presence of naiural 
phenomena; and that instead of book-learning he per- 
mitted the fulness of Nature herself to opera e upon his 
open mind. The disadvantages are, perhaps, of a sub- 
ordinate kind ; but they reveal themselves in quite as un- 
mistakeable a manner when he strives to give expression 
to his ideas; and to supply, by all kinds of sensuous 
imagery, the want of mathematical culture. This is 
manifestly the way in which he alighted upon his Lines 
of Force, his Ray Vibrations, and other notions, which 
bewildered the investigators of his time, and the truer 
and clearer meaning of which has been in part mad: out 
by mathematical theory since Faraday himself ceased 
from his labours. 
“ And still, in this unlearned son of a smith, who held 
fast throughout his life the pious creed of his fathers, 
ran a vein of philosophy which gave him the right 
to be ranked among the foremost of those engaged 
in the general intellectual travail of our age. That 
