NATURE 
[NoveMBER 12, 1Sgu 
Ephemerts for Berlin Midnight. 
1896. , R.A. Deel. Log A. Br. 
ae m. 
Nov. 10... 20 9'6 +19 3 0°206 1'0 
Te see ZOU 530 laces 16 12 219 bie) 
Mop eee ZO TBs} a LBA ee i eRe 10 
2 ee LOGS i2 nes 1) 246 09 
26) meen 09) 55°90 >. rasp do 259 o'9 
Prof. Holden has also communicated elements calculated from 
observations made on November 2, 3, and 4. These are some- 
what different from those given above, but the computed posi- 
tion for November 18 is not far from that given in the above 
ephemeris, being R.A. 20h. 1°8s., Decl. 13° 57’. 
On the roth the comet was nearly in a straight line, joining 
5 and y Sagittee, being about as far from + as 6 is, only on the 
opposite side. The motion in declination is in the direction of 
a'Aquila, near which star the comet will be found on the 26th. 
Tue Leonips.—In a preceding number of NATURE (vol. liv. 
p- 623), Mr. Denning gave full information for those wishing to 
observe this star shower with the naked eye, but, curiously 
enough, he did not mention the great advantage photography 
would afford us in obtaining a very accurate determination of 
the radiant point. One can quite understand that, by placing a 
small camera on a telescope equatorially mounted, and employ- 
ing a wide angle lens oriented towards the radiant point, a large 
space in the sky can be included on the plate sufficient to catch 
many of the streaks if they be at all numerous. The plates can 
be changed every thirty minutes or so. It was the intention of 
the writer of this note, some fourteen days ago, to adopt this 
principle, and he has already been able to get the necessary 
apparatus ready. The use of a wide angle lens necessitates 
that, if an equatorial be used, the camera must be placed at the 
extreme end (object-glass end) of the telescope, otherwise the 
opening in the shutters will cut off some of the field, and in con- 
sequence neutralise to some extent the value of the wide angle. 
This was found to be so ; but, by the kindness of Mr. J. Norman 
Lockyer, a siderostat was placed at his disposal. The instru- 
ment not having yet been set up since its return from the eclipse 
expedition, it was erected temporarily ina good position open 
towards the eastward. 
Captain Abney has very generously lent a Cooke’s lens, 
invented by Mr. Dennis Taylor, giving a field of about 75° and 
of about five inches focal length, so that only now fine weather 
is required. 
It may be mentioned that the current (November) number of 
The Observatory contains an interesting article by Dr. Johnstone 
Stoney on the ‘* Leonids,” in which he quotes an extract from 
a letter received from General Tennant, who advises practically 
the same method described above. The appendix to this article 
contains a reference to the literature on the subject of the 
Leonids, from which we make the following summary. 
Prof. H. A. Newton, Sz//iman’s Journad, 1864, vols. xxxvii. 
and xxxviil. pp. 377 and 53 respectively. Prof. Adams, Comptes 
vendus, March 25, 1867, p. 651, and Monthly Notices R.A.S., 
April 1867, p. 247. Signor Schiaparelli, Les Jondes, December 
1866, and beginning of 1867. English outline of Schiaparelli's 
work, by Prof. Newton, Phzlosophical Magazine for July 1867, 
p. 34. M. Le Verrier, Com/tes rendus, January 21, 1867, 
p- 94. Dr. Johnstone Stoney, AZonthly Notices R.A. Se June 
1867, p. 271, and Philosophical Magazine, September 1867, 
p. 188. 
Sunspots, COMETS, AND CLIMATE VARIATIONS. —A problem 
of considerable interest is suggested by the paper which Herrn 
Johannes Unterweger contributes to vol. Ixiv. of the Devk- 
schriften der Math. Natur. Wissen. Classe der Kats. Akad. 
der Wess. of Vienna. The pamphlet, which has been printed 
separately, is entitled, ‘*‘ Ueber zwei Trigonometrische Reihen 
fiir Sonnenflecken, Kometen und Klimatschwankungen,” and 
contains a preliminary statement of the investigation in question. 
The main result of the work is that there seems to be found a 
striking similarity between the variations of a certain function 
obtained from periodic comets near perihelion and the curves 
illustrating sunspot and climate variations. This function is 
obtained from a formula (see Denxkschriften Kats. Akad. Ween., 
vol. lix.) that he has previously published, which gives a 
relationship between the function and the inclinations and 
perihelion distances of well-observed periodic comets. The 
comets dealt with are divided into two groups, according as their 
perihelia he to the north or south of the solar equator, and the 
NO. I411, VOL. 55| 
mean of those which pass through their perihelia during each 
year is taken. The author then finds two trigonometrical series 
which represent the periods of both sunspot frequency and the 
variations of this cometary function, the former of which includes 
a secular variation of about 70 years, while the latter indicates a 
35-year variation corresponding with that due to climate varia- 
tions. In the curves shown, Herrn Unterweger indicates a 
variation in the minima as well as in the maxima in the case of 
the calculated frequency of sunspots, the former of which does 
not really occur as observation shows. The investigation is, 
however, full of interest, and perhaps the more detailed dis- 
cussion which he promises will throw more light on this question. 
THE EXPLOSIVE PROPERTIES OF 
ACETYLENE. 
N view of attempts to extend the use of acetylene as an 
illuminant, the disastrous explosion in Paris, to which refer- 
ence was made in our issue of October 22, has created a good 
deal of anxiety in this country. In this connection it may 
interest our readers to have a further account of the memoir on 
the explosive properties of acetylene recently presented to the 
French Academy by MM. Berthelot and Vieille (see NATURE, 
vol. liv. p. 591). 
The authors state that in acetylene at ordinary pressures 
neither an electric spark, nor a flame, nor an explosion of 
fulminate will cause more than a local dissociation of the gas (a 
fact already established by Prof. H. B. Dixon), but that if the 
gas be compressed beyond two atmospheres, the dissociation, 
once started, is propagated without sensible diminution through- 
out the whole mass of gas. In this way dissociation of the gas 
was effected in a tube 20 millimetres in diameter and 4 metres 
long. The acetylene splits up into pure hydrogen and a friable 
mass of carbon, which forms a cast of the containing vessel, and 
can be withdrawn intact. At a pressure of 20 atmospheres, 
which is about half the tension of the saturated vapour of liquid 
acetylene at 20°C., the explosion develops a tenfold pressure, 
but the rate of propagation is much below that of true explosive 
wave of sucha mixture as electrolytic gas. The temperature 
due to the explosion at this pressure is calculated to be 2750° C. 
As the violence of the explosion increases with increasing initial 
compression, it was to be expected that liquid acetylene would 
exhibit the character of a ‘“‘high” explosive. This MM. 
Berthelot and Vieille have shown to be the case. Eighteen 
grammes of liquid acetylene exploded in a steel bomb of 49 c.c. 
capacity by a hot wire developed a pressure of 5564 kilogrammes 
per square centimetre. This corresponds to an explosion pres- 
sure for the liquid alone of about 9500 atmospheres—a value 
approaching that of guncotton. The decomposition of liquid 
acetylene by simple ignition is relatively slow, and appears to 
take place in two stages, one corresponding to the decomposition 
of the gas, the other that of the liquid. In an experiment where 
the liquid occupied ‘15 of the containing vessel, a maximum 
pressure of 1500 kilogrammes per square centimetre was re- 
corded. 
Experiments were made to determine whether the compressed 
gas or liquid could be exploded by mechanical shock. The 
results were, strictly speaking, negative. Neither by fall, nor 
crushing with a ram, nor by the impact of a bullet which pierced 
the containing cylinder, was the acetylene exploded. In the 
case of liquid acetylene, an explosion followed the shock after a 
short interval, but this was shown to be due to the ignition of 
the escaping gas, after admixture with air, by a spark from the 
breaking metal. A small charge of fulminate of mercury fired 
in the middle ofa cylinder of liquid acetylene detonated the liquid, 
and shattered the cylinder in the manner of a true explosive. 
The authors describe the conditions under which danger may 
arise by casual elevation of temperature during the manipulation 
of acetylene. In the first place they note that in generating 
acetylene by the action of a small quantity of water or excess of 
calcium carbide in a closed vessel, the carbide may become in- 
candescent and lead to the detonation of the gas. At least one 
accident due to this cause has already been recorded. Sudden 
compression of the gas in filling cylinders, or in admitting it into 
a reducing valve, may likewise raise the temperature to the point 
of danger. A sharp mechanical shock breaking the containing 
vessel may cause sparks capable of firing the explosive mixture 
formed by the escaping gas with the external air. 
In conclusion MM. Berthelot and Vieille express their opinion 
