JUNE 29, 1899] 
It was found that the rates of diffusion of the positive and 
negative ions differed more when the gas was dry than when it 
was moist. 
Values of « tn Square Centimetres per Second. 
qg 
) 
« for + ions | « for —ions | « for + ions | « for —ions 
Gas in dry gas in dry gas | in moist gas in moist gas 
Air "0274 042 032 7035 
Oxygen : 025 0396 | ‘0298 | 0358 
Carbonic acid... 023 026 "0245 | ‘o256 
Hydrogen 123 *190 Zoe 142 
| 
From the equation of motion 
1 pu sake + nXe 
K ax 
(where # is the partial pressure of the ions, x the number of 
ions per c.c., e the charge on each ion, X the electric force at 
any point, and w the velocity of the ion in the x direction), it 
can be seen that when a = 0 the velocity 2, due to the electric 
ES 
force X, is nXex. 
If the potential gradient is one volt per centimetre, X = 1 
‘ aa 320 
in electrostatic units, and the corresponding value of w is 
ke 2 
“= = 
300 
Let N be the number of molecules per c.c. in a gas at pres- 
sure P, equal to the atmospheric pressure and temperature 
15 C., the temperature at which ~, and « were determined. 
The quotient a may be substituted for” in the above equa- 
tion, and Ne is therefore obtained in terms of qualities which 
can be determined experimentally. 
2 8 
Ne=3 1° eae since P = 10° in C.G.S. units. 
K 
Substituting for #, the mean velocities given by Prof. Ruther- 
ford (E. Rutherford, Pz? Aag., November 1897), and for « 
the mean coefficient of diffusion obtained for the dry gases, and 
the following values of Ne are obtained :— 
Air os. Nene be rOL” 
Oxygen ... Neo = 1°25 101” 
Carbonic acid Nés = 1-30 101” 
Hydrogen Nex = 1'00 101° 
Experiments on electrolysis show that one electrodynamic 
unit of electricity in passing through an electrolyte gives off 
1°23 c.c. of hydrogen at temperature 15° C. and pressure 10° 
C.G.S. units. The number of atoms in this volume is 2°46 N, 
so that if E is the charge on an atom of hydrogen in the liquid 
electrolyte 
2°46 NE=1 electrodynamic unit of quantity 
=3 10!” electrostatic units. 
Hence NE=1'22 10)", the charge E being expressed in 
electrostatic units. Since N is constant, these numbers show 
that the charges on the ions produced by Rontgen rays in air, 
oxygen, carbonic acid, and hydrogen are all the same, and equal 
to the charge on an atom of hydrogen in a liquid electrolyte. 
Prof. J. J. Thomson (J. J. Thomson, Phz/. Mag., December 
1898) has shown that the charge on the ions in oxygen and 
hydrogen, which have been made conductors by Rontgen rays, 
is 6 10~” electrostatic units, and is the same for both gases. 
_ Taking this value for the charge e, the number of molecules 
in a cubic centimetre of a gas is obtained : 
IN=2: 101%) 
The weight of a molecule of hydrogen ne therefore 
4°5 10-* grammes. 
In order to prove that the positive and negative ions have 
the same charge, the ratio of the coefficients of diffusion must 
be shown to be equal to the ratio of the velocities. This sub- 
NO. 1548, VOL. 60} 
NATURE 
212 
ject has been investigated by Prof. Zeleny (J. Zeleny, //z/. 
Mag., 1898), and it was found that the negative ion travels 
faster than the positive ion in air, oxygen and hydrogen, the 
ratio of the velocities being 1°24 for air and oxygen, 1°15 for 
hydrogen, and 10 for carbonic acid. 
Royal Society, June 15.—‘‘On the Orientation of Greek 
Temples, being the Results of some Observations taken in 
Greece and Sicily in the month of May 1898.” By F. C. 
Penrose, M.A., F.R.S. 
The orientation of the Cabeirion Temple, near Thebes, 01 
which the angle has been disputed (see p. 46 in my paper of 
1897), was remeasured with the theodolite in May 1898, and 
the previous observations confirmed. An additional example 
is added from an archaic Temple of Neptune in the Isle of Poros, 
introducing the employment of the bright zodiacal star Regulus, 
which I had not before met with. 
In Sicily the re-examination of the temples at Girgenti, 
where, in my former visit, I had relied for azimuth on the sun’s 
shadow and the time, has enabled me to give to the elements 
some amendments in detail, the only point of consequence being 
that the orientation date of the temple named Juno Lacinia is 
brought within the period of the Hellenic colonisation of that 
city. 
The most interesting point in the paper seems to be, that in 
the case of two Athenian temples, namely, the Theseum and the 
later Erechtheum—z.e. the temple now partially standing—it 
is shown that the days of those months on which the sunrise, 
heralded by the star, illuminated the sanctuary coincided 
exactly, on certain years of the Metonic cycle, with the days of 
the Athenian lunar months on which three important festivals 
known to be connected with at least one of those temples were 
held. The years so determined agree remarkably well with the 
probable dates of the dedication of those temples ; and in the 
case of the first mentioned, the festival, which was named The 
Thesea, seems to leave little doubt that the traditional name of 
the temple, which has recently been much disputed, is the 
correct one. 
‘*Collimator Magnets and the Determination of the Earth’s 
Horizontal Magnetic Force.” By C. Chree, Sc.D., LL.D., 
F.R.S., Superintendent of the Kew Observatory. Com- 
municated by the Kew Observatory Committee of the Royab 
Society. 
During the last forty years, there have been examined at Kew 
Observatory upwards of toocollimator magnets used in observing 
the horizontal force and declination. 
The ‘‘constants”” of these magnets—temperature and induc- 
tion coefficients, and moment of inertia—have been determined 
at the Observatory, and the tables based on these determinations 
have served to reduce magnetic observations at a large number 
of the leading magnetic observatories. 
The present paper deals with the data recorded in the 
Observatory books for the constants specified above, and with. 
other quantities—such as the ‘‘permanent ” magnetic moment— 
which are deducible from the records. It determines the mean: 
values of the several quantities for the instruments of the leading: 
English makers, and investigates whether relations do or do not 
exist between them. It then deduces from the records the 
probable errors in the values of the several quantities, proceeding 
on the hypothesis that the methods of determining them are 
correct. It next examines, from a mathematical standpoint, 
the accuracy of the formulz employed in reducing horizontal 
force observations, and, from a physical standpoint, the possi- 
bility of differences between the quantities determined at the 
Observatory and the quantities actually concerned in horizontak 
force observations. 
The various sources of uncertainty are dealt with, and an 
attempt is made to ascertain to what extent they may affect the 
values found for the horizontal force. 
The results of the paper are of too technical a character to. 
admit of their being summarised briefly in an intelligible way. 
Physical Society, June 23.—Mr. T. H. Blakesley, Vice- 
President, in the chair.—A paper on the magnetic hysteresis of 
cobalt, by Prof. Fleming, Mr. A. W. Ashton, and Mr. H. G. 
Tomlinson, was read by Mr. Ashton. A rectangular sectioned 
circular ring of cobalt was insulated with silk tape and wound 
over with four secondary coils put on at quadrantal positions. 
Over these secondary coils six primary coils were placed, and 
the ring was submitted to a complete set of magnetic tests with 
a ballistic galvanometer. From these observations various 
