| Fuly 21, 1870] 
number of thirty-seven and a half millions should be contained 
. 
A 
\ 
+ 
a 
er 
in about two drachms of water, as quoted by Tyndall, from 
Mr. Dancer’s examination,* it is probable that the whole or 
repeated units of such millions might be harmlessly swallowed. 
But for the most part the supposed germs were not germs of 
any kind, but broken scraps of vegetable and animal tissues, 
spiral vessels from dried horse-dung, hairs, wings, and legs of 
insects, detrita of dress, and the like. ‘The results were, in fact, 
entirely negative of any peculiar bodies to which the epidemic 
disease could be referred. One general result arrived at at that 
time, however, agrees with the observation of Tyndall in his 
recent investigation of dust by a beam of light—viz., that the 
floating particles in the air are chiefly of an organic nature. 
__ This we might have been prepared for, from the specific weight 
of dried organic material, enabling such dust to float, when the 
heavier inorganic substances would be deposited. That the 
infectious diseases spread by emanations from the sick, must 
have been long known, and that such emanations are of a solid 
nature, we may infer from the fact that they may be dried and 
conveyed from place to place; but in what state, whether as 
amorphous material or as germs, we know no more to-day than 
was known a thousand years past. No new fact bearing upon 
the propagation of contagious disease has been reached by the 
recent investigations on dust; nor can we infer the nature of 
summer catarrh because the nasal mucus under such circumstances 
and at no other time, was found peopled by vibriones, since de- 
composing mucus is always populous with this common race of 
infusoria. ‘Che phenomena of fermentation and putrefaction in 
dead and decomposing substances afford no explanation of the 
changes observed in a living body in a fever process. The 
purulent matter produced in small-pox, is not, as we know, in 
any way comparable to the yeast formed in fermenting fluids. 
On the contrary, the microscope demonstrates that the forms, as 
for instance in yariolous pus, are not different from those con- 
tained in other purulent and innocuous exudations. Nor have 
we any reason to conclude that any forms which are observed are 
germs which convey the disease. It is to be regretted that a 
confusion in terms has been made, Instead of dust and disease 
it ought rather to have been dust and putrefaction, or dust and 
fermentation, since the relation of dust to disease has not been 
revealed anywhere in the inquiry. That the air conveys the 
material causes of the infectious diseases from the sick to the 
healthy, is a notorious fact, which had equal force before these 
inq:tiries were instituted, though, owing to the exigencies of social 
intercourse, a fact more neglected than in times of comparative 
ignorance. — It is difficult to vindicate exactness in progress with- 
out seeming to beat the same time a hinderer of it. The onward 
and the regulating forces of a machine, though not incompatible, 
but necessary, require the nicest balance. ‘This reflection sug- 
gests itself by the way the spread of infectious diseases has been 
handled. The theories it has given rise to haye been so easily 
put forward as to thereby create distrust. But the spirit of 
science is no fayourer of negations. ‘Der Geist der stets 
yerneint’ finds no greater friend in medicine than in theology. 
Still it will be admitted that no progress can be made by the 
ready acceptance of every proposition, however distinguished the 
source from which it emanates. The parasitic origin and nature 
of epidemics may be true, but it has yet to be proved, As an 
hypothesis, it admits of proof or disproof, and so has further 
claim upon the industry of those who have put it forward as a 
suggestion, Without going to the length which this hypothesis 
demands, we must admit, howéyer, that we know enough to 
uide us much further than we have yet gone in .the practice of 
prevention.” 
PROFESSOR TYNDALI’S LECTURES AT THE 
ROVAL INSTITUTION, ON ELECTRICAL PHE- 
NOMENA AND THEORIES 
PROF . Tyndall completed a short course of seven lectures 
at the Royal Institution, on Thursday, June 9th, upon 
**Electrical Phenomena and Theories,” which were made as 
interesting as all his lectures are, by the ingenuity and complete- 
ness of the experimental illustrations ; in this particular case the 
apparatus of his distinguished predecessor, Faraday, being 
largely drawn up, in addition to considerable accessions of more 
recent date, many of them derived from the kind help of indi- 
yiduals who have made themselves high reputations in the various 
* Proceedings of the Royal Institution of Great Britain, Jan, 21, 1870. 
NATURE © 
243 
branches of Electrical Science. The scope of the Professor’s 
demonstrations covered the entire range of Electrical and Mag- 
netic Science, commencing with the phenomena of yoltaic 
electricity, and passing through the various leading manifestations 
and peculiarities of electro-magnetism, magnetic force, frictional 
electricity, electro-chemistry, magneto-electricity, and, of course, 
electric telegraphy, and the relations of electric motive force to 
heat. 
One remarkable peculiarity in these lectures of Professor 
Tyndall is, the effective way in which several of the more 
subtle effects of electrical change and power are made manifest 
to a large audience by the instrumentality of beams of electric 
light, manipulated in various ways. ‘Thus, for instance, the 
elongation of a solid bar of iron, when it is thrown into the 
magnetic state, by being encircled in the folds of a voltaic 
current, conveyed by a helix, is shown by the starting of a spot 
of light, some six or eight inches upon a screen, when the 
molecular condition of magnetism is excited by the passage of 
the current. A beam of light falls upon a small mirror, carried 
at the extremities of the arm of a lever, so resting upon the end 
of the iron bar, that when the lever is lifted by the magnetic 
elongation of the bar, the beam of light is shot off from the 
mirror as a long weightless index. The change in the position 
of the molecules of iron by the action of magnetism is also 
proved by throwing the beam through a vertical cell of glass, 
containing magnetic oxide of iron suspended_in water. When 
the cell is exposed to the influence of the poles of a strong 
electro-magnetic, the light passing through the cell and con- 
tained liquid to a screen beyond, brightens, in consequence of 
the metallic molecules turning themselves ‘‘end on” to the 
incidence of the beam. The lines of magnetic force assumed, 
when iron filings are sprinkled over the poles of a magnet, are 
portrayed by the intervention of a system of lenses, which de- 
picts the image upon the screen. The formation of the “‘ tree of 
lead” upon the negative electrode of a voltaic current, when a 
salt of lead is decomposed by the current, is shown in the 
same way; the arborescent crystals glowing and dissolving alter- 
nately on the opposite poles, immersed in the solution as the 
direction of the current is reversed. The very beautiful colours 
and patterns of Nohili’s rings, formed when lead is thrown down 
by voltaic decomposition upon a polished plate of steel, are ex- 
hibited by a similar intervention of lenses, and the illumination 
from the electric beam. An artificial telegraph cable, whose 
resistance to the transmission of the electric current is made 
identical with 14,000 miles of an actual marine cable, is formed 
by introducing into the path of the current gaps, consisting: of 
feebly conducting liquids and condensers, so distributed as to 
represent the respective distances by telegraphic route of Gibral- 
tar, Malta, Suez, Aden, Bombay, Calcutta, Rangoon, Singapore, 
Java, and Australia. A mirror, belonging to each gap, lies in 
the path of the currents, carried by a galvanometer, constrained 
to deflect its needle from the position of both on the instant that 
the passage of the current is felt. Before the current is sent 
through the apparatus, ten dots of light, cast from the mirrors by 
the instrumentality of electric illumination, lie upon the screen, 
in a straight vertical range. When the current is passed through 
the apparatus, dot after dot starts aside upon the screen, as the 
current fills the condenser immediately before each mirror, and 
then flows beyond to deflect the galvanometer immediately in 
advance. ‘The deflection of the successive galvanometers, and 
the corresponding traverse of the beam of light upon the 
screen, is seen, under this arrangement, to take place at succes- 
sive steps or intervals, which exactly express the intervals of 
time which the electric current would require to reach the 
several stations named, in the actual progress of telegraphy. 
The starting aside of spot after spot upon the screen when the 
current is sent through the apparatus, and the subsequent return 
of spot after spot to the position of original test in inverse order, 
forms a very striking illustration of the fact that the resistance ot 
an electric cable is in some degree dependent upon its length, 
and that time is consumed in overcoming this resistance. The 
most interesting and telling of all these beam-of-light illustrations, 
however, is certainly the one which is employed to indicate the 
excitement of diamagnetic force in a tube of copper, when it 
is suspended between the poles of an electro-magnetic. The 
tube is carried by a string of silk, and rotates rapidly under the 
influence of a twist given to the string. The string also carries 
above the tube a series of small mirrors, which reflect the light 
of an electric beam, so that a continuous elliptical band of 
illumination is formed on the screen whilst the twisting is con- 
