Juty 27, 1899] 
ve NRL 
395 
that produced by air, being only about 6°6 volts, or about 
34 volts lower than when the hissing was caused by air alone. 
In order to exclude all possibility of doubt as to the effect of 
the various gases, I repeated the experiments with the arc 
entirely enclosed in one of the fire-clay crucibles, so that the 
only gases that could reach the crater were those blown down 
the tubular positive carbon. The current was distinctly below 
the hissing point, being only 10 or 11 amperes, and the arc 
was from 2 mm. to 3 mm. long. 
The results were exactly the same as with the open arc, 
except in the case of hydrogen. For air and oxygen produced 
hissing and a sudden diminution of the P.D., and nitrogen and 
carbon dioxide had no such effect, even when the current was 
very much increased. But whereas, as has been previously 
stated, hydrogen produced a distinct hissing of its own when 
blown down the positive carbon in the ofe air, it produced 
none when used in the same way with the arc eveclosed in the 
crucible. 
To prove that, in order to produce the sudden diminution of 
P.D under discussion, it was necessary for the active gas to 
actually ouch the crater, a tubular wega/zve carbon was used, 
and each gas was blown up through it in turn, gently enough 
not to force the gas directly against the crater. 
In zo case was there any sudden diminution of the P.D., 
whatever gas was employed, and whether the are was open or 
enclosed. On the contrary, there was generally a small increase, 
probably due to the lengthening of the arc by its being blown on 
one side. If oxygen or air were blown very hard up the neg- 
ative carbon, they would either produce hissing, or blow the arc 
out, or both; for in that case some of the gas got to the crater 
uncombined with the carbon vapour, and acted exactly as if it 
had been blown do~n the tubular positive carbon. 
The case, then, stands thus : 
(1) When the are begins to hiss in the ordinary way, the 
P.D. between the carbons diminishes by about 10 
volts. 
(2) If the air is excluded from the arc, this diminution of 
the P.D. does not take place, even when the current 
is nearly three times as great as would cause hissing 
in the air. 
(3) If, however, while the air is excluded, puffs of air are 
sent against the crater, the diminution of the P.D. 
does occur, even with currents much syad/er than 
would cause hissing in the air. : 
(4) If, instead of air, oxygen is sent against the crater, the 
P.D. is diminished to exactly the same extent as 
when air is used. 
(5) If, on the other hand, 2z¢vogen is sent against the crater, 
no diminution of the P.D. is observable. 
(6) If air or oxygen is gently blown through the xega/zve 
carbon, so that it cannot get direct to the crater, 70 
diminution of the P.D. follows. 
Thus there can be no shadow of doubt that the sedden 
diminution of P.D. that accompanies the hissing of the open 
arc ts due to the oxygen in the arr getting directly at the crater 
and combining with the carbon at its surface. 
It only remains to show how the actual hissing sowsd may be 
produced by the burning of the surface of the crater. The 
moment this burning begins, a cloud of gas, formed of the pro- 
ducts of combustion, must spread over the crater, protecting it 
momentarily from the action of the air as effectually as the 
carbon vapour had hitherto done. When this gas is dispersed, 
the air will again come in contact with the crater, a fresh cloud 
will form, and the whole action will start de xovo. Thus a 
series of rushes and stoppages of the air will take place, setting 
up an irregular vibration of just the kind to cause a hissing 
noise. Not only this, however, but since the crater must cease 
to burn each time that it is protected by the gas, the diminution 
of P.D. must also cease to exist, since its cause is removed, and 
the P.D. will therefore rise momentarily. Thus an oscillation 
of the P.D. between the carbons, and, consequently, of the 
electric current, must be created, corresponding with the oscil- 
lation of the az current. 
These oscillations of both air and electric currents do actually 
exist with the hissing arc. The first I have proved by means of 
a fine asbestos fibre fastened at one end to the hole in the 
crucible (Fig 8) through which the positive carbon moved. 
The asbestos ring was raised, and the space between the 
carbon and the crucible was left clear, and was made large 
enough to allow the free end of the short fibre to stretch out 
NO. 1552, VOL. 60] 
horizontally between the two. When the arc was silent, the 
fibre scarcely moved, but the moment hissing started it set 
up a vigorous vibration, instead of being sucked into the 
crucible as it would have been if there had been a steady inward 
current of air. 
Messrs. Frith and Rodgers (Phz7. Mag., 1896, p. 420) 
showed, in 1896, that the e/ectvz: current was oscillatory with 
the hissing arc, and Messrs. Duddell and Marchant (/ow: 2. 
Inst. Elec. Engs., vol. xxviii. p. 84) in the account of their 
beautiful experiments with the oscillograph, have given actual 
curves of the P.D. and current with the direct current hissing 
arc, showing distinctly the oscillations in both. 
Thus the direct contact of the oxygen of the air with the crater 
of the positive carbon is capable of producing, not only the 
diminution of the P.D. between the carbons of the arc, which is 
) the most striking accompaniment of hissing, but also every other 
important manifestation connected with it, including the sound 
itself. HERTHA AYRTON. 
THE INTERNATIONAL CONFERENCE ON 
HYBRIDISATION AND CROSS-BREEDING. 
JN this country where the application of biological principles 
to the industries which they underlie is left as a rule to 
private enterprise or the half-hearted interest of County Councils, 
any means whereby the scientific worker is shown to be useful 
to the practical man is a help towards a better state of things. 
For this reason alone the Conference on Hybridisation sug- 
gested by Mr. W. Bateson, and held on July 11 and 12, under 
the auspices of the Royal Horticultural Society, may have more 
importance in the future than Prof. Henslow claimed for it in 
the present. The more immediate results that will accrue are 
those which the Society foresaw must arise if the attempt to call 
forth papers, remarks and exhibits dealing with hybridisation 
wasat all successful. Two days were not many to devote to the 
meeting, and it is a matter of surprise that such an amount of 
work was done in the time. When, however, the whole of the 
contributions, whether read or unread at the conference, are 
published in the form of an illustrated report, the Royal Hortt- 
cultural Society should be more than satisfied. 
Nevertheless the question of hybridisation is so large, as 
Mr. Engleheart said in the discussion, that ‘‘ whole sets of 
subjects ’’ (graft hybrids, for instance) could not even be touched 
upon, and the suggestion made in several quarters, but by the 
American delegates in particular, that a supplementary con- 
ference be heldin another country should be taken up seriously. 
Before discussing the chief points of the meetings it may be 
of interest to give a list of the speakers and their subjects. 
Tuesday, July 11, in the Society’s Gardens at Chiswick :— 
(1) Maxwell T. Masters, F.R.S., Introductory remarks as 
Chairman, 
(2) W. Bateson, F.R.S., ‘‘ Hybridisation and Cross: breed- 
ing as a Method of Scientific Investigation.” 
(3) A. de la Devansaye, *‘ Hybrid Anthuriums.” 
(4) Prof. Hugo de Vries, ‘‘ Hybridisation as a means of 
Pangenetic Infection.” 
(5) The Rev. Prof. Henslow, ‘‘ Hybridisation and its Failures.” 
(6) C. C. Hurst, ‘‘ Experiments in Hybridisation and Cross- 
breeding.” 
Wednesday, July 12, at the Town Hall, Westminster. 
(1) The Rev. Prof. Henslow, Introductory remarks as Chair- 
man. 
(2) Herbert J. Webber, ‘‘ Work of the United States De- 
partment of Agriculture in Plant Hybridisation.” 
(3) Dr. J. H. Wilson, ‘‘ The Structure of certain New Hybrids 
(Passiflora, Albuca, Begonia, &c.)” 
(4) R. Allen, ‘* Hybridisation viewed from the Standpoint of 
Systematic Botany.” 
(5) Henry de Vilmorin, ‘‘ Hybrid Poppies.” 
(N.B.—Nos. 2 and 3 were illustrated by means of lantern slides, 
and No. 5 by large water-colour drawings. ) 
(6) Discussion ; Prof. Henslow, Mr. Burbidge, Rev. G. H. 
Engleheart, Mr. George Paul, Mr. Bunyard, Dr. 
Masters, Mr. Willet Hays, and Mr. W. Cuthbertson. 
The United States was represented by Mr. Herbert Webber, 
of the Department of Agriculture, his colleague Mr. Swingle, 
and Mr. Willet Hayes; France by MM. de la Devansaye 
