Fan. 19, 1871] 
NATURE 
237 

Irrigation,” by F. C. Danvers. An account of the advantages 
that would result to agriculture from a system of irrigation, ren- 
dered necessary by the destruction of forests, irrespective of the 
question of the utilisation of sewage. 4. ‘‘ War Science,” by 
H. Baden Pritchard. A statement of the instruction in War 
Science given in the Royal Artillery and Royal Engineers, and 
of recent improvements in gunnery, illustrated especially by the 
Scott and Moncreiff gun-carriages ; the improved modes of manu- 
facturing gunpowder ; and the invention of the electric torpedo in 
conjunction with the Abel fuse. 5. ‘‘ Spectra of Metallic Com- 
pounds,” from the Journal of the Franklin Institute. 6. ‘On 
the various Tints of Autumnal Foliage,” by H. C. Sorby. A 
very interesting paper, in which the writer details the results of 
his experiments on the various colouring matters of leaves, &c., 
which he classifies as follows :—(1) chlorophyll, or the green 
colouring matter ; very rarely found pure, even in fresh leaves ; 
insoluble in water, but soluble in alcohol or bisulphide of carbon; 
the spectra have all a very well-marked absorption band in the 
red, but the green is more or less completely transmitted, so that 
the prevailing tint is a more or less modified green ; (2) the xav- 
thophyll, or yellow group; insoluble in water, but soluble in 
alcohol and in bisulphide of carbon; the spectra show absorption 
at the blue end, often with more or less well-marked narrow 
bands ; but the red, yellow, and yellow-green are freely trans- 
mitted, so that the general colour is clear yellow or orange ; (3) 
erythrophyll, or the red colouring matter ; soluble in water and 
aqueous alcohol, but not in bisulphide of carbon; show strong 
absorption in the green part of the spectrum ; (4) chaysophyll, or 
the golden-yellow group ; soluble in water and aqueous alcohol, 
but insoluble in bisulphide of carbon, with variable spectra ; (5) 
the phaiophyll group, comprising various browns; soluble in‘water, 
but not in bisulphide of carbon ; do not give well-defined absorp- 
tion-bands. Mr. Sorby gives the following scheme of the rela- 
tive abundance of these various groups of colours as the ieaves 
advance towards decay. 
Complete vitality  eetlagl athe cna | 
and growth. . Chlorophyll . . / 
Low vitality and 1S ge : \ 
change Xanthophyll . . 
Death and de- {Fraiceyil 
composition. . (Humus . 
7. ‘*On the Relations between Chemical Change, Heat, and 
Force, with a special view to the economy of electro-dynamic 
engines,” by the Rey. H. Highton. Contests the theory gene- 
rally accepted that a certain amount of chemical change corre- 
sponds and is interchangeable with a certain amount of heat and 
electric force ; and that this heat again corresponds and is inter- 
changeable with a certain amount of work or mechanical energy. 
The author considers that the whole subject requires a fresh, 
strict, and full experimental investigation. He then refers to the 
many different answers that have been given to the question, 
What is the mechanical equivalent of heat? and holds that it 
has never been proved that there is any such equivalent. He 
details in support of his view the conflicting results obtained from 
the elaborate experiments with a galvanic battery by such experi- 
menters as M. Favre, M. Sorel, M. Weber, M. Kohlrausch, and 
Mr. Gore. ; 8. ‘‘Our Patent Laws.”—The pages devoted to 
** Progress of the Sciences ”’ again embrace Physical Science only, 
Physics, Chemistry, and Mechanics—an inequality which will 
doubtless be rectified in future numbers. 
More or less bright green. 
More or less green-brown, 
More or less red-scarlet. 
} \ More or less bright orange-brown. 
{ Less or more dull brown. 


SOCIETIES AND ACADEMIES 
LONDON 
Royal Society, January 12.—‘‘Some Experiments on the 
Discharge of Electricity through Rarefied Media and the Atmo- 
sphere.” By C. F. Varley.—After the labours of Mr. Gassiot, one 
approaches this subject with diffidence, lest he should appear to be 
attempting to appropriate the glory which so justly belongs to that 
gentleman and to Professor Grove. The nature of the actioninside 
the tube is at present involved in considerably mystery, but some 
light is thrown upon the subject by the following experiments. 
Before describing them, however, the author wishes to observe 
that he has seen Mr. Gassiot’s last papers, * and finds that, so far 
as regulating the strength of the current is concerned, he has been 
proceeding in a similar manner to the author. The tube princi- 
pally used in these experiments contains two aluminium wire 
rings, the one 74; inch in diameter, the other 7%, and separated 
* Proc. Roy. Soc., vol. xi. p. 329, & vol. xii. p. 329. 

to inch, the tube 1} inch in diameter, 31 inches in length ; it was 
one of Geissler’s manufacture, was very well exhausted, and pro- 
fessed to contain hydrogen. A U-shaped glass tuhe containing 
glycerine and water was placed in circuit. Two aluminium wires 
inserted in this tube gave a ready means of reducing or augment- 
ing the resistance at pleasure. Glycerine affords an easy means 
of producing very great resistances. The battery used in this ex- 
periment was a Daniell’s battery, each cell having a resistance of 
from 50 to 109 Ohms. The resistance of the glycerine-and-water- 
tube was between 2 and 3 megohms ; this latter resistance was 
made large, in order that the resistance of the tube and battery 
might be neglected without entailing error. The following law 
was found to govern the passage of the current :—1st. Each tube 
requires a certain potential to leap across, 2nd, That having 
once established a passage for the current, a lower potential is 
sufficient to continue the current. 3rd. If the minimum potential, 
which will maintain a current through the tube, be P, and the 
power be varied to P+1, P +2, &c. to P+, the current will vary 
instrength, as 1, 2, &c. #. The following Tables (I. and IT.) illus- 
trate this ; there is a little irregularity in the figures due to the 
irregularity of the battery, although it was recharged for the 
occasion. 




TABLE I. 
I. 2. 30 | 4. 
Cells of Daniell’s Observed Deflections of M ard Col. 
Battery, P + 7. Reflecting Galvanometer. can. | diviced by 7. 
307 = P+ 3 ° ° ° ° ° | ° 
308 = P+ 4 5 st 5h 54 13 
309 = P+ 5 9 9 9 9 9 18 
3zio=P+ 6 12 12} 12 12} 12} 204 
311 = P+ 7 t4 14 Ac 14 2 
31z2=P+ 8 16 “i 80 16 2 
313—P+ 9 17418 18 17} 107 
314=P+10 mepe) aks Be oe 19k 195 
315—P+11 21% 21 22 214 21h 195 
316= P+12 234 234 23¢ .. 233 | 1°96 
317—= P +13 sas 25 1°96 
318 =P + 14 27k. 27k | x97 
319 = P+ 15 29s ss 293 | 1°97 
320 =P+16 314 «31% «= 3 31 34 | 1°05 
*323=P + 19 B7e, 38S OPA W375 374 | 197 
325= P+ ar 40 4t 40k 4y | 1°94 
330 = P+ 26 5r 5 le 5r 1°96 
335 =P + 31 60} 604 60} 1'95 
340 = P + 36 7O 70 7° 1°94 
345 =P +41 793 79% 794 1°94 
550=P + 46 89 8g 89 1°94 
355=P+51 984 984 98$ 193 
300 = P+ 56 108 = 108 108 1°93 
365= P+ 6r m8 118 118 1°04 
370 = P+ 66 128 86128 128 194 
375=P+71 139 ©6140 1.9} 196 
380 = P+ 76 150 150 150 1°97 
TABLE II. 
304=>P+ 0 ° we . ° ° 
305=P+ 1 2 2 oe | 2 ie 
306 = P+ 2 4 4 - 4 2 
307—P+ 3 ° 6 6 2 
308 = P+ 4 8 8 8 2 
309 = P+ 5 10 10 TO | 2 
3r0—=P+ 6 | 12 12 rz." | 2 
320=P +16 314 32 ; 31; 1'97 
330 = P+ 26 5I 5I 51 1°96 
340 = P + 36 7 718 eee 1'97 



It thus appears that a certain amount of power is necessary to 
spring across the vacuum ; after that it behaves as an ordinary 
conductor, excluding that portion of the battery whose potential 
is P, and which is used to balance the opposition of the tube. 
In these experiments P was 304 cells. ‘The tube in question 
could not be persuaded to allow a current of less than 323 cells 
to pass ; but when once the current had established a channel, 
on lowering the potential by shor? circuiting portions of the bat- 
tery, so as not to break the circuit, the current would flow when 
the battery was reduced to 308 cells. By, however, passing a 
current from 600 cells through the second tube W, filled with 
pure glycerine, and offering several thousand megohms resist- 
ance, an extremely feeble current, too weak to affect the galva- 
nometer, kept a channel open by its passage ; with this arrange- 
ment the figures in Table II. were obtained, which are more 
regular at the commencement, and a power of P +1 would pass 
*This power,”-23, was the lowest at which the current would jump, 
