244 
NATURE 
[Fuly 21, 1870 
tinued. The instant the electro-magnet is made active by the 
transmission of the current through its helix, the copper tube 
acquires diamagnetic polarity by induction, and under the 
influence of this polarity the rotation is arrested, and the band of 
lights upon the screen is changed into a small stationary spot of 
illumination. When the electro-magnet is unmade by the 
arrest of the voltaic current, the spot of light again becomes an 
elliptical band, under the resumption of the twisting of the silk 
string with its mirrors and copper tube. 
Of the numerous other very pleasing and telling illustrations 
exhibited in these lectures, space only permits allusion to be 
made to a very few which have been selected from the series, 
as being worthy of especial mention. The sound produced by 
the molecular vibration in iron when its mass is transiently mag- 
netised by the voltaic current, is made audible by suspending 
an iron poker upon two sounding boards, and making it the 
core of a helix, conveying an electric current, An assistant is 
converted into an extemporised electrophorus, by flapping his 
black coat with fur while he stands upon a glass-legged stool. 
Small fish of gold leaf are made to float in the air current given 
off from the knob of a charged Leyden jar. A thick drinking 
glass is shattered by the expansion of the water contained in it, 
when sparks formed under the intensifying power of fifty con- 
densers joined ‘‘in cascade,” and primarily charged by a 
voltaic battery of one thousand cells, are passed through the 
liquid. To demonstrate the relation of resistance to heating 
power, a long line of wire is arranged in alternate links of 
platinum and silver, and when a voltaic current of due intensity 
is passed through the length, each stretch of the platinum wire 
is seen to glow with brilliant red heat, while the stretches of 
silver wire between remain still invisible. A beautiful series of 
Geissler’s vacuum tubes were brought into successive operation, 
in which the auroral discharge was broken into stratified leaves, 
in which the glow was extinguished by the approximation of 
the poles of an electro-magnet, in which a feeble glow was con- 
verted into bright stratified light by the influence of a magnet ; 
and beautiful beyond all the rest, the light from the enclosed 
negative terminal of the voltaic battery was arranged into the 
well-known lines of magnetic force, when subjected to the in- 
fluence of the poles of a magnet. 
It would be unnecessary in alluding to these very admirable 
_ lectures, to say one word of Prof. Tyndall’s clearness and power 
as an expositor of the phenomena of Physical Science, These 
are now well known to the hundreds who are attracted to 
Albemarle Street on the frequently renewed occasions when the 
Professor performs this portion of his functions asa lecturer of the 
Royal Institution. It is, however, well worth while to draw 
attention to a device which the Professor adopts, with the 
happiest effect, to render his lectures as complete in their in- 
struction as they can be made, He prints a series of well- 
digested ‘‘ Notes” of the entire range of the subjects he passes 
over in each lecture, has them placed in the hands of each indi- 
vidual as he enters the lecture room, and then refers from time 
to time to the systematic outline, as occasion suggests the ex- 
pediency of doing so. By this procedure the Professor is able 
to give full attention and time to each step of his illustrative 
demonstration, without being hampered with the need of telling 
everything that he has marked out beforehand—an extremely 
difficult thing to accomplish in a brief unextensible interval, 
where wiva voce teaching has to be employed. Under this 
management any broken or omitted link in the full argument is 
readily recovered by glancing the eye over the range of printed 
notes after the conclusion of the lecture. This plan is well 
worthy of adoption, wherever popular lectures upon science are 
delivered to large audiences, with a view to instruction as well as 
amusement. 
ZOOLOGY 
Plateau on the Flight of Coleoptera 
M. Fetix PLATEAU has supplemented the recent labours of 
Marey and others upon the flight of insects by examining the 
movements of the wings of certain Coleoptera. Specimens of 
the common May-beetle and Ovyctes zasicornis were selected for 
experiment. The apparatus used consisted of two pulleys, 
fastened one above the other, at a distance of two centimetres, 
on a vertical support ; the upper pulley made twelve tums for 
each one made by the lower, and could be caused to rotate 
twenty-four times ina second, The insects were killed by ether 
vapour immediately before each experiment; and the wings 
could be fastened, by a simple contrivance, to the front pro- 
longation of the axis of the upper pulley. 
A wing, in its folded state, was fixed on the instrument in such 
a manner that its plane made, with the plane of rotation, an 
angle of 45°, asin the living animal. On tuming the pulleys, it 
struck the air obliquely by its upper surface and front margin ; 
but the small diameter of the apparently continuous revolving 
disc (as indicated by a graduated scale) proved that the wing 
was still folded, and that centrifugal force had not affected it. 
When rotation was produced in an opposite direction, so that 
the wing struck the air both by its posterior membranous margin 
and inferior surface, the increasing diameter of the disc gave 
proof of the expansion of the wing, which, indeed, continued to 
be much extended when motion was arrested. When the plane 
of a wing was perpendicular to the plane of rotation, and the 
revolution of the wheel was such that the wing struck the air 
by its dorsal or upper surface, no extension ensued ; when it 
struck by its lower surface, only partial extension followed. 
Now the oblique, not the perpendicular plane is that chosen by 
nature, and is, as has been seen, much more favourable for flight. 
On fixing an open wing on the axis so as to make an angle 
with the plane of rotation, and turning in one direction, the 
wing remained open; on reversing the direction (#¢. acting on 
the upper surface) it became partially closed. 
SCIENTIFIC SERIALS 
In the Revue des Cours Scientifigues for July 9, we have an im- 
portant article on the Axioms of Geometry, by Prof. Helmholtz, 
which has, however, already appeared in an English form in the 
Academy, and the translation of an article by Mr. E. J. Reed, 
on Navires blindés ; while M. Bernard concludes his course on 
Suffocation by the Fumes of Charcoal. In the number for 
July 16 there is an address by M. Dumas, delivered before the 
Academy of Sciences in honour of M. Pelouze, which occupies 
nearly the whole of the number, leaving room for only a short 
abstract of M. Bienaymés paper read before the Academy, on 
the military mortality in the Italian campaign of 1859-60. : 
Annales de Chimie e de Physique, May, 1870.—‘* Researches 
on the Gaseous Products of the Combustion of Coal,” by M. A. 
Scheurer-Kestner. This important paper commences with an 
historical notice of experiments on this subject by Péclet, Ebel- 
men, Debette, Commines de Marsilly, Ebelmen and Sauvage, 
Foucou and Amiguis, and Cailleet, pointing out several causes of 
inaccuracy which are to be traced in their researches, The author 
then describes the process employed by him in collecting and 
analysing the gases from the flue of a steam boiler, Through the 
brickwork of the furnace a hole was bored, and in it was placed 
a platinum tube about 700 millimetres long and ten in diameter. 
To one end of this tube a copper pipe surrounded by a Liebig’s 
condenser is soldered, the other end being closed witha plug. A 
narrow slit extends the whole length of the platinum tube, so that 
the air drawn through it is an average specimen of the gas in the 
flue. It is found also that the gas must be slowly aspirated 
through the slit in order to obtain a fair average of the gas pass- 
ing through the flue during a considerable space of time. The 
author connected the apparatus with a water aspirator, by which 
he drew zss Of the total gas which passed up the chimney 
through the platinum tube ; at the same time, from 54, to 54; of 
the aspirated gas was removed by a branch and collected in a 
bottle of three litres capacity, from which mercury was allowed 
to flow very slowly. Thus about spy'suo Of the gas in the chim- 
ney was collected over mercury, and with this the analyses were 
performed. For the analytical processes we must refer the reader 
to the original paper, merely pointing out the conclusions at 
which the author has arrived. The gases of the chimneys were 
almost always found to contain carbonic oxide and’ hydrocarbons, 
even in the presence of oxygen arising from excess of atmospheric 
air. It was also found that the quantity of carbon lost in the 
form of smoke in the presence of sufficient air was about 4 per 
cent., and that the loss of carbon as combustible gases does not 
exceed 2 or 3 per cent. when the excess of air amounts to 30 per 
cent. or more. The paper concludes wita a section on the theory 
of the formation of smoke in the presence of an insufficient quan- 
tity of air, in which the author discusses the observations of 
Sainte-Claire Deville on dissociation, and of Berthelot on the 
action of heat on hydrocarbons, and points out their application 
to this subject, 
