Oct. 1, 1885 | 
NATURE 
Se, 
change of the electromotive force). The quantity » has never 
been experimentally determined, but two hypotheses have been 
made as to its value by Maxwell and Helmholtz. According to 
Maxwell 7 = «/4m, where « is the specific inductive capacity, 
and, according to Helmholtz, 7 is also a function of x. There 
is very little experimental evidence for either of these theories. 
For Maxwell’s theory, perhaps the best evidence is that, if we 
assume the electro-magnetic theory of light, the refractive index 
should, if 7 = «/47, equal the square root of a specific inductive 
capacity, which is very approximately the case for a good many 
substances. Maxwell's assumption has the great advantage of 
getting rid of all discontinuity in the currents ; and, when this 
is the case, all forms of the potential theory lead to the same 
result. So that, if we could prove Maxwell’s theory experi- 
mentally, it would be a complete theory of electro-dynamic 
action. If it should turn out, however, that Maxwell’s theory 
is not true, then we should have to go on further and determine 
which of the several forms of the potential theory is the true one ; 
as, if the currents are not closed, the different forms of the 
theory lead to different results. It would seem that the most 
important thing to be done in electro-dynamic theory is to de- 
termine whether 7 = «/47 or not, and the author has des_ribed 
two ways in which this may be done. If Maxwell’s theory 
should prove not to be true, we must go on to determine the 
value of for all dielectrics, and which of the forms of the 
potential theory is the true one. 
Report on Standards of White Light.—Various experiments 
have been made by the Committee. The members have come 
to the conclusion that the standard candle as defined by Acts of 
Parliament is not in any sense a standard. The spermaceti 
used is not a definite chemical substance, and is mixed with 
other substances. Also the constitution of the wick is not 
properly defined. The Committee have considered the relative 
merits of different proposed standards, and have come to the 
conclusion that for comzer.ia/ purposes the pentane standard of 
Mr. Vernon Harcourt is the best. Although the Committee 
wish their opinion on this point to be known to the Board of 
Trade and the public, they do not recommend the adoption of 
any particular standard until further experiments on radiation 
have been made. Several experiments are enumerated which 
they propose to make. They ask reappointment, with a grant 
of 50/. towards the proposed researches. 
Report of the Committee on Meteoric Dust.—Experiments have 
been made at the Scottish Marine Station by means of an 
apparatus in which the wind blows through gratings of fine 
platinum wire. The moisture deposited is collected and 
examined for suspended particles. Funnels have also been 
placed at different localities for catching rain. The presence of 
carbonaceous matter is most marked. In smaller quantities 
occur quartz, felspar, mica, tourmaline, garnet, glassy particles 
resembling Krakatoa dust or pumice, and small round magnetic 
particles about 1—5ooth of an inch in diameter, They resemble 
similar larger particles got from deep-sea deposits at the greatest 
distance from continental land. None are of cosmic origin. 
Usually they have a small nucleus in the interior, but are fre- 
quently hollow. Further observations are to be made at various 
stations all over the world. 
Report of the Committee on Meteorological Observations on Ben 
Nevis.—The chief additional observations made during the 
year were with regard to rainfall and wind. Vhe amount of 
water substance deposited, in whatever form, has been collected 
by specially-designed gauges and measured every hour since 
June 24, 1884. In the end of October the anemometers designed 
by Praf. Chrystal were added to the instruments. But during 
seven months—-November, 1884, to May, 1885—no anemometer 
could indicate results, with the exception of thirty days. This 
is owing to the deposition of ice-crystals. The greatest speed 
indicated during three days was on the night of April 24. The 
mean speed for 12 hours was 74 miles per hour, the speed for 
one particular hour being 81 miles per hour. The highest tem- 
perature reached, 60°'1 F., occurred at 2 p.m., August 9; and 
the lowest, r1°"1 F., at midnight, February 16. The coldest 
week—average temperature, 16°°2 F.—was the one ending on 
February 21. The changes of temperature, particularly in 
winter, were caused, not by direct solar influence, but by the 
passage of cyclones or anticyclones over the observatory. Indeed 
in the stormy months of winter this may be taken to be accu- 
rately the case. In summer the afternoon minimum ot atmo- 
spheric pressure was 0007 inches above the mean for the whole 
day, but in winter it was below the mean. During twelve 
months there were 464 hours of sunshine, being about 11 per 
cent. of the total possible amount. Heavy rainfalls frequently 
occur. The longest for one hour was on December Io, 1884. 
The largest daily fall occurred then also, being 4°264 inches. 
On an average, a fall of at least one inch occurred one day in 
seven. 
Report of the Committee on Solution, Secretary Dr. W. W. 
J. Nicol.—lhe subjects discussed in this Report are ;—(r) 
Molecular volumes, (2) saturation, (3) supersaturation, (4) vapour 
pressures, and (5) expansion of salt solutions. (1) The results 
of a series of experiments show the molecular volume of a salt 
in dilute solution to be a quantity composed of two constants : 
one for the metal and the other for the salt radical ; hence the 
same volume change is produced by replacement of one metal 
or salt radical by another metal or salt radical. Wa'er of crys- 
tallisation is not to be distinguished from the solvent water, but 
the water of constitution possesses a volume different from that 
of the rest of the water—results showing the existence in solu- 
tion of the anhydrous salt in contradistinction to the view that 
a hydrate, definite vr indefinite, is formed in solution. (2) 
Saturation is reached when the further addition of salt would 
produce diminution of the mean molecular volume of the mole- 
cules already present. (3) The so-called supersaturated solu- 
tions are simply saturated or non-saturated solutions of the 
anhydrous salts, the only truly supersaturated solutions being 
those which result from the fact that, when a hot solution-is 
cooled, a finite time is required for the excess of salt to crystallise 
out, 
The Report of the Committee appointed to investigate by means of 
Photography the Ultra-violet Spark Spectra emitted by Metallic 
Elements and their Combinations under Varying Conditions, 
drawn up by Prof. Hartley, F.R.S., was presented by him to 
the Section; in it an account is given of the results of the 
investigation of the changes in the character of the spectra of the 
metals produced by variation in the strengths of the solutions of 
their salts—e.g. chlorides, nitrates, or sulphates. The study of 
a very considerable number of the photographs of such spectra 
shows the strength of the solution to have a marked effect on 
their character, the more dilute the solution the smaller the 
number of lines; further, that under the same spark con- 
ditions, similar solutions of the same strength emit the 
same spectrum. Solutions containing I per cent., 1I-1oth, 
1-1o0o0th, and I-1oooth of the metal were used ; solutions of the 
latter strength seldom gave a spectrum of more than three or 
four lines, and with solutions containing less than r-roth per 
cent. the diminution in the number of lines is usually very 
marked. The spectrum reaction may be utilised for the quanti- 
tative analysis of minerals, and yields results more reliable than 
those obtained by ordinary methods. The reaction is extremely 
delicate, and in the case of magnesium one part of the metal in 
10,000 millions of solution can be detected by the appearance of 
two characteristic lines. 
Third Report of the Committee, consisting of Profs. Williamson, 
Dewar, Frankland, Crum Brown, Odling, and Armstrong, 
Drs. Hugo Miller, F. R. Fapp, and H. Forster Morley, and 
Messrs. A. G. Vernon Harcourt, C. E. Groves, F. Millar 
Thomson, H. B. Dixon (Secretary) and V. H. Veley, re- 
appointed for the purpose of drawing up a Statement of the 
Varieliis of Chemical Names which have come into use, for 
Indicating the Causes which have led to their Adoption, and for 
Considering what can be done to bring about some Convergence 
of the Views on Chemical Nominclature obtaining among English 
and Forcign Chemists.—An account of the authorship of some of 
the various systems of nomenclature which have been devised 
for the purpose of distinguishing between compounds formed by 
the union of the same elements in different proportions has 
been given in the “* Historical Notes” prefixed to the Second 
Report of this Committee. Among these systems the use of 
the termination ows and zc, to denote respectively lower or higher 
degrees of saturation of one element or group with another 
element or group, is perhaps that which has met with the 
widest acceptance. This system further directs that when 
electro-negative groups, the names of which end in ews and zc, 
unite with electro-positive groups to form salts, these termina- 
tions are to be changed into 7¢e and ave respectively. It would 
be ill-advised to attempt on etymological grounds to change a 
system so firmly established as that involved in the present use 
of the prefixes Zyfo and hyfer. No ambiguity can arise from 
