AuGuST 29, 1912] 
NATURE 
669 
observations made at Helwan, the first order station 
of Egypt. The size of this part has been considerably 
reduced by the omission of observations for every 
hour and the publication of the results in a more 
summarised form. This part also includes an im- 
portant paper by Mr. H. E. Hurst on the reduction 
of the observations of terrestrial magnetism. (2) 
Climatological tables, including rainfall and river 
gauge observations. The chief features of the year 
were the heavy rainfall in April and October, and the 
high Nile flood, which began early and was about 15 
per cent. above the normal; the rainfall was, how- 
ever, deficient in Egypt generally. With regard to 
relative humidities, it is found that the values in the 
Sudan computed from Jelinek’s tables (Leipzig, 1903) 
not uncommonly fall below 10 or even 5 per cent. 
As it seems improbable that the surface air is ever 
so dry as this, the validity of the tables in extreme 
conditions is under consideration. A first order station 
for the Sudan is in course of formation at the Gordon 
College, Khartoum. 
In a publication of the Egyptian Survey Department 
entitled ‘‘ Magnetic Observations made during 1911 
at the Khedivial Observatory, Helwan,’ particulars 
are given of the mean monthly and annual values of 
the magnetic elements at Helwan during 1911, and 
of the diurnal variations in declination and in hori- 
zontal and vertical intensity for each month and the 
year. Days of incomplete record and those of dis- 
turbance character ‘‘2,”’ on the international scale, are 
omitted, the days actually utilised being 330 for 
declination, 317 for horizontal, and 291 for vertical in- 
tensity. Particulars are given of eight disturbances— 
occupying parts of thirteen days—in which the range 
of the horizontal intensity exceeded o’001 C.G.S. The 
largest ranges observed were o’00188 in horizontal 
intensity, o°’00044 in vertical intensity, and ry’ in 
declination. 
We have received from the publishers (Messrs. A. 
Hermann et Fils) an interesting tract by MM. C. 
Jordan and R. Fiedler on convex closed curves, and 
others connected with them. The topic was suggested 
by questions of probability, and we are occasionally 
reminded of the work of Crofton, one of the great 
authorities in this field. But probability is not actually 
treated here; the main part consists of tangential polar 
formula and discussion of derived curves such as 
pedals, parallel curves, &c. On p. 34 there is an 
interesting figure such as is often produced in a street 
by one wheel of a cart which has twice turned round. 
Each turn generally involves a slight backing, and 
then the trace of the inner wheel contains two 
adjacent cusps and an ordinary node. Various 
examples due to Euler, Kepler, Newton, &Xc., are given 
as illustrations. 
A merHop of detecting the presence of polarised 
light in the light from a sky obscured by thick clouds 
is described by Mr. A. E. Oxley in the July number of 
the Proceedings of the Cambridge Philosophical 
Society. It depends on the use of a Babinet com- 
pensator, with its principal direction set at 45° to 
that of the observing Nicol, and of a special rhomb in 
NO. 2235, VOL. 89] 
front of the compensator which allows part of the 
incident light to pass without change while it intro- 
duces a phase difference of 7/2 into the remainder of 
the beam. When the edges of this rhomb are parallel 
| to the principal direction of the Nicol, bands are seen 
in the field of view even when the amount of polarised 
light present is too small to produce colours in a 
selenite plate, and the apparatus also allows the mean 
plane of polarisation of the incident light to be 
ascertained. 
In the June number of the Bulletin de la Société 
d’Encouragement pour l’Industrie nationale, M. A. 
Verneuil describes a form of muffle or crucible furnace 
suitable for laboratory work up to a temperature of 
1600° C. If a crucible is to be heated, it is sur- 
rounded by a cylindrical block of refractory material 
which rests on a brick pillar and is provided with a 
lid which leaves openings for the escape of the burnt 
gas. The gas is introduced into the space between 
the crucible and its surrounding cylinder by a passage 
which is tangential to the inner surface of the cylinder 
at the point of entry. By this means the jet of gas 
' and compressed air is given a spiral form and a higher 
temperature is attained, while the durability of the 
furnace is increased. The idea of the spiral flame 
seems worthy of general adoption in furnace design. 
OUR ASTRONOMICAL COLUMN. 
ASTRONOMICAL OCCURRENCES FOR SEPTEMBER : 
SEPTEMBER 3. 13h. 57m. Saturn in conjunction with 
the Moon (Saturn 6° 20’ S.). 
th. 22m. Neptune in conjunction with 
the Moon (Neptune 5° 43’ S.). 
», 16h. om. Mercury at greatest elonga- 
tion W. of the Sun (17° 58’). 
8. 20h. 59m. Venus in conjunction with 
Mars (Venus 0° 30! N.). 
g. th. om. Mercury in conjunction with 
a Leonis (Mercury 0° 5/ N.). 
» 7h. 15m. Mercury in conjunction with 
the Moon (Mercury 3° 18’ S.). 
~ 
rr. 21th. 43m. Mars in conjunction with 
the Moon (Mars 0° 4’ N.). 
12. th. 1m. Venus in conjunction with the 
Moon (Venus 0° 41’ N.). 
16. 3h. om. Saturn stationary. 
» 13h. 33m. Jupiter in conjunction with 
the Moon (Jupiter 4° 54’ N.). 
20. 15h. 13m. Uranus in conjunction with 
the Moon (Uranus 4° 34’ N.). 
22. 22h. gm. Sun enters Sign of Libra. 
Equinox. 
25. 23h. 45m. Moon eclipsed, invisible at 
Greenwich. 
30. gh. 22m. Saturn in conjunction with 
the Moon (Saturn 6° 20’ S.). 
Tue Varrapitity ofr Poraris.—The confirmation of 
the variability of the pole star, by the selenium photo- 
meter method, is announced by Mr. Joel Stebbins in 
No. 4596 of the Astronomische Nachrichten. He ob- 
served the star for light-changes in 1904 with a 
polarising photometer, but difficulties prevented a 
definite conclusion being arrjved at for so small a 
variation as o'1l0o mag. Again in 1910 he attempted to 
find the variability with the selenium photometer, but 
meeting with difficulty in the selection of a suitable 
comparison star, postponed the research. 
