March 17, 1870| 
NEAT CREE, 
501 
the foregoing experiments is not of the same brightness 
throughout its entire transverse section. Pass a white 
switch, or an ivory paper-cutter, rapidly across the beam, 
the impression of its section will linger onthe retina. The 
section seems to float for a moment in the air as a 
luminous circle with a rim much brighter than its central 
portion. The core of the beam is thus seen to be en- 
closed by an intensely luminous sheath. An effect com- 
plementary to this is observed when the beam is inter- 
sected by the dark band from the platinum wire. The 
brighter the illumination, the greater must be the relative 
darkness consequent on the withdrawal of the light. 
Hence the cross section of the sheath surrounds the dark 
band as a darker ring. 
The following four paragraphs, though printed nearly 
two months ago, have not been published hitherto. Might 
I say that whatever my opinion on the subject of “spon- 
taneous generation” may be,1 purposely abstain from 
expressing it here? That expression shall be given at the 
proper time. I desire now to show the practical value of the 
luminous beam as an investigator of the state of the air. 
The question of ‘‘ Spontaneous generation” is intimately con- 
nected with our present subject. On this pot a kind of polar 
antagonism has long existed between different classes of investi- 
gators. Wan Helmont gavea receipt for the manufacture of mice, 
and it was for ages firmly believed that the maggots in putrefying 
flesh were spontaneously produced. edi, a member of the 
famous Academy del Cimento, destroyed this notion by proving 
that it was only necessary to protect the meat by a covering of 
gauze to prevent the reputed generation, In 1745 two very able 
men, Needham and Spallanzani, took opposite sides in the dis- 
cussion, the forming affirming and the latter denying the fact of 
spontaneous generation. At the beginning of our own century, 
_ we find on the affirmative side Lamarck, Oken, and J. Miiller ; 
and on the negative Schwann, Schultze, and Ehrenberg. The 
chief representatives of the two opposing parties in our day_are 
Pouchet and Pasteur. 
The method of inquiry pursued in this discourse will, I think, 
help to clear the field of discussion. The experimenters do not 
seem to have been by any means fully aware of the character of 
the atmosphere in which they worked ; for if this had been the 
case, some of the experiments recorded would never have been 
made. For example, to make the destruction of atmospheric 
germs doubly sure, M. Pouchet, the distinguished supporter of 
the doctrine of spontaneous generation, burnt hydrogen® in air 
and collected the water produced by the combustion. Even in 
this water he afterwards found organisms. But supposing he 
had seen, as you have, the manner in which the air is clouded 
with floating matter, would he have concluded that the deport- 
ment of water which had been permitted to trickle through stich 
air could have the least influence in deciding this great question? 
I think not. Here is a quantity of water produced and collected 
exactly as M. Pouchet produced and collected his. This water 
is perfectly clear in the common light ; but in the condensed 
electric beam it is seen to be laden with particles, so thick-strewn 
and minute, as to produce a continuous cone of light. In passing 
through the air the water loaded itself with this matter, and 
hence became charged with incipient life. * 
Let me now draw your attention to an experiment of Pasteur, 
which I believe perplexes some of the readers and admirers of 
that excellent investigator. Pasteur prepared twenty-one flasks, 
each containing a decoction of yeast, filtered and clear. He 
boiled the decoction, so as to destroy whatever germs it might 
contain, and while the space above the liquid was filled with 
pure steam he sealed his flasks with a blow-pipe. He opened 
ten of them in the deep, damp caves of the Paris Observatory, 
and eleven of them in the courtyard of the establishment. Of 
the former, one only showed signs of life subsequently. In nine 
out of the ten flasks no organisms of any kind were developed. 
Tn all the others organisms speedily appeared. 
Now here is an experiment conducted in Paris, which shows 
* In this case a polished silver basin was soldered to one end of a wide 
brass tube ; the tube was filled with ice, the hydrogen flame was permitted 
to play upon the basin, and the water of condensation was then collected. 
_Dr. Child also objects to Pouchet’s experiment. 
that the air of one locality can develop life when the air of 
another locality cannot. Let us see whether we cannot here in 
London justify and throw light upon this experiment. I place 
this large flask in the beam, and you see the luminous track 
crossing it from side to side. The flask is filled with the air of 
this room, charged with its germs and its dust, and hence capable 
of illumination. But here is another similar flask, which cuts a 
clear gap out of the beam. It is filled with unfiltered air, and 
still no trace of the beam is visible. Why? By pure accident I 
stumbled on this flask in our apparatus room, and on inquiry 
learnt that it had been a short time previously taken out of one 
of the cellars below stairs. Other flasks were in the same cellar. 
I had three of them brought up to me; they were optically 
empty. The still air had deposited its dust, germs and all, 
and was itself practically free from suspended matter. You can 
now understand the impotence of the air of the Paris caves. 
The obseryation illustrates at once the influence of the germs 
and the accuracy of Pasteur. 
The air of the cellar was afterwards examined by the 
electric lamp. Though less heavily charged than the air 
outside, it was by no means free from particles. This was 
to be expected, because the door of the cellar was frequently 
opened. The flasks themselves were the true tranquil 
chambers ; on their sides the dust had been deposited, 
and to them it firmly clung. ‘To prove this several flasks 
about ten inches in diameter were filled with common air, 
corked, and laid upon a table in the laboratory. After 
two days’ quiet they were optically empty. 
Nor is it necessary even to cork the flasks ; for with their 
mouths open the air within them is scarcely disturbed, 
certainly not displaced. Two days’ rest on one of the 
laboratory tables suffices to deposit the organic dust and 
to render the open flasks optically empty. 
I have had a chamber erected with a view to experi- 
ments on this subject. The lower half is of wood, its 
upper half being enclosed by four glazed window-frames. 
The chamber tapers to a truncated cone at the top. It 
measures in plan 3 ft. by 2ft. 6in., and its height is 5 ft. roin. 
On the 6th of February this chamber was closed, and 
every crevice that could admit dust or cause displacement 
of the air was carefully pasted over with paper. The 
electric beam at first revealed the floating dust within the 
chamber as it did in the air of the laboratory. The 
chamber was examined almost daily; a perceptible 
diminution of the floating matter being noticed on each 
occasion. At the end of a week the chamber was opti- 
cally empty, exhibiting no trace of matter competent to 
scatter the light. But where the beam entered, and 
where it quitted the chamber, the white circles stamped 
upon the interior surfaces of the glass showed what had 
become of the dust. It clung to those surfaces, and from 
them instead of from the air, the light was scattered. If 
the electric beam were sent through the air of the Paris 
Caves, the cause of its impotence as a generator of life 
would, I venture to predict, be revealed. 
It cannot, I think, be doubted that the method of 
observation here pursued is destined to furnish useful 
control and guidance in researches of this nature. 
Royal Institution, March 14 J. TYNDALL. 
HEREDITARY GENIUS 
Hereditary Genius, an Inguiry into its Laws and Con- 
sequences. By Francis Galton, F.R.S.,&c. (Mac- 
millan & Co.) 
N this book Mr. Galton proposes to show that a man’s 
natural abilities are derived by inheritance, under 
exactly the same limitations as are the form and physical 
