JUNE 10, 1915] 

NATURE 
409 

plates taken at an interval of from 15 to 20 years. 
The largest proper motion found by this examination 
is 1-0” annually belonging to B. D. 77°, 361, a star of 
g:2m. visual and 109m. photographic magnitude. 
Heliographic Observations.—In the year ended May 
10, photographs of the sun were obtained on 239 days. 
The mean daily spotted area of the sun was 140 
millionths of the sun’s visible hemisphere during 1914, 
as against 8 in 1913, 37 in 1912, and 64 in 1911, thus 
showing the usual rapid rise from minimum. 
Magnetic Observations—The mean values of the 
magnetic elements for 1914 and three previous years 
are as follows :— 
Y Declination souzontal Di 
ear orce In 1p 
EC.G.S. units 
IgII Ts 33-0 0185492 66 52 “6 (3-in. needles) 
IgI2 15 24:3 0185487 6651 46 ,, % 
1913 TGs 2h O218534.7) GONSONetin) \5, 39 
{66 49 27 ~~, ” 
nor Tee O8518 6G 51 13 (dip inductor) 
The new magnetograph house appears to be per- 
fectly satisfactory. The arrangements for maintaining 
constancy of temperature have so far worked well, 
the indication of a set of maximum and minimum 
thermometers showing differences of only a_ small 
fraction of a degree Fahrenheit during periods of 
several weeks between successive visits of the observer 
to the chamber for the purpose of making scale deter- 
minations. 
Meteorological Observations—The mean tempera- 
ture for the year 1914 was 508°, or 1:3° above the 
average of the 70 years 1841-1910. For the 12 months 
ended April 30, 1915, the mean temperature was 50:2°. 
During the 12 months ended April 30, 1915, the 
highest temperature in the shade (recorded on the 
open stand in the enclosure of the magnetic pavilion) 
was 92-1° on July 1. On 21 days the highest tempera- 
ture in the shade equalled or exceeded 80°. The 
lowest temperature of the air recorded during the same 
period was 22:3° on January 23. There were 36 days 
during the winter on which the temperature fell as 
low as 32:0°. 
The mean daily horizontal movement of the air in 
the year ended April 30 was 288 miles, which is 4 miles 
above the average of the previous 47 years. The 
greatest recorded daily movement was 791 miles on 
December 4, and the least 75 miles on April 11. The 
greatest recorded pressure to the square foot was 
26:3 Ibs. on December 28, and the greatest velocity in 
an hour 55 miles on the same day. During the year 
1914, Osler’s anemometer showed an excess of 11 revo- 
lutions of the vane in the positive direction N., E., S., 
W., excluding the turnings which are evidently acci- 
dental. 
The number of hours of bright sunshine recorded 
during the r2 months ended April 30, by the Campbell- 
Stokes instrument, was 1573 out of a possible 4457 
hours, giving a mean proportion of 0-353, constant 
sunshine being represented by 1. This is above the 
average amount, principally on account of a fine June 
and a fine September. 
The rainfall for the year ended April 30 was 24-73 
inches, being o-61 inch greater than the average for 
the period 1841-1905. The number of rainy days 
(0-005 inch or over) was 171. September with 0-73 inch 
was the driest month and December with 6-02 inches 
the wettest; it was, in fact, the wettest December in 
the Greenwich series, and the three winter months, 
with 12-86 inches, the wettest winter in 100 years. 
Clocks and Time Service.—The daily time signals 
2 The values given in last year's report have been increased by 207, 
arising from a redetermination of the moment of inertia of the deflecting 
magnet. 
NO. 2380, VOL. 95] 



from the Eiffel tower have been regularly observed by 
Mr. Lewis and Mr. Bowyer. The mean of the times 
as observed by Mr. Lewis is +0-026s. late on Green- 
wich time from 209 observations, and by Mr. Bowyer 
+0-043s. late from 280 observations. The difference 
of a quarter of a second between the Eiffel Tower 
signal and the time as determined by the transit circle 
which existed two years ago appears to have been the 
personal equation of the standard observer as com- 
pared with the new impersonal micrometer. 
The accuracy of the time-balls at the Admiralty 
signal stations and of the Westminster clock is shown 
by the following table of the errors of the return- 
signals received at Greenwich. 
Apparent Error of Return Ports- Port- Devon- West- 
ignal s. mouth land port minster 
Not greater than 0-2 27 a 2e Tei 2 OB) oir 
Between 0:2 and o-5 13 12 14 28 
ni) 0-5 5, 10 I oO A 05 
Greater than 1-0 ) Co) Oo 74 
The Westminster clock was on two occasions only 
found to be more than 3-os. in error. 

RADIO-THERAPY- ITS SCIENTIFIC BASIS 
AND ITS TEACHING. 
Gels recent discovery that X-rays and y rays can 
be defracted into spectra by the natural grating 
contained in the orderly structure of crystals, sets at 
rest the question as to the nature of these radiations. 
They are of the same nature as light-waves, but of 
very much higher frequency—from 10,000 to 100,000 
times as high. 
The certitude of the identity of these three classes of 
radiation leads to issues of much importance to 
medical science. For medicine had for many years 
been invoking the aid of the mysterious X and y rays 
without in the least knowing what these agents were. 
It now turns out that they are physically identical 
with light. This fact secure, medical science is made 
heir to the discoveries of photo-electric science. I 
shall briefly restate the leading facts of this science 
On the living cell y or X-rays produce remarkable 
effects. The study of these effects in plants dates 
back several years. Schobert, Errera, Molisch, 
Guilleminot, and others have contributed to it.2 The 
rays may retard cell division, and more especially 
affect the germinating embryo. They may kill such 
cells. They may also in very feeble doses promote 
cell division. Gaskell has specially studied the effects 
of X-rays on the embryonic cells of the chick. He 
found that up to a certain amount of exposure the 
embryo may make complete recovery from the in- 
jurious effects of the rays, but that there is a critical 
dosage beyond which recovery does not occur and 
development stops. The efiects of ultra-violet light in 
setting up mitosis in certain cells of the eye are beau- 
fully shown in experiments by E. K. Martin (Proc. 
Roy. Soc., B85, July, 1912, p. 319). Certain ultra- 
violet rays—the Schumann rays—are said to be always 
very destructive in their action on living protoplasm, 
giving rise to cytolysis and death in the cases of 
spirogyra, amoeba, and other unicellular organisms, 
in less than one minute. These wave-lengths, which 
are about half the length of visible rays in the violet, 
are rapidly absorbed even in air. It has been sug- 
1 Based on a paper read to the members of the Dublin Clinical Club. on 
March 16, by Prof. J. Joly, F.R.S. Reprinted with abbreviations and some 
revision from the Scientific Proceedings of the Royal Dublin Society, vol. 
xiv., No. xxxvii. 
2 Le Radium,” vii., 1910, p. 247- 
3 Gaskell, Proc. Roy. Soc., Ser. B, vol. Ixxxiii., February, rgrr1, p. 305- 
