56 
NALEORE, 
[NOVEMBER 19, 1903 
case of three Arctic foxes from Iceland in the Zoological 
Gardens, of which ‘‘ one turns perfectly white every winter, | 
while the other two remain dark.” 
Cambridge, November 12. W. F. LancuesTeEr. 
The Magnetic Storm of October 31. 
Dr. GLAzEBROOK has asked me to send you a copy of one 
or more of the magnetic curves during the late storm, and 
also of a characteristically ‘‘ quiet *’ day. For the latter I | 
Ai 
KEW HORIZONTAL FORCE 1903 
Seta cen DRT ree NE 
eee 
KEW PATTERN HORIZONTAL FORCE MAGNETOGRAPH. 
) OCT. 29, 0 401030, 10374". GMT. 
|. 90,10 38 t03/, 1064", 
ment, which was partly lost on our own magnetograph, 
the scale of ordinates of which is more open. In _ this 
curve I mm. represents in the original very nearly 1/ of are, 
and increasing ordinate decreasing westerly declination. 
We had not set the clock driving this instrument quite 
correct, and the times shown in the trace are about four 
minutes wrong. 
During the rapid movements the traces on the originals 
are faint, and consequently are not fully shown in the 
photographic copies sent you. 
I ought to: explain that the slight 
blurring and want of clearness on the 
horizontal force trace October 29-31 
really arise from the electric trams. 
Their action, however, is hardly visible 
during the storm proper in either de- 
clination or horizontal force. In- the 
vertical force, however—of which no 
copy is sent—the electric tram disturb- 
ance is much more considerable, and 
Ae 
ey might easily be mistaken by the un- 
& 5 initiated for a fairly active magnetic 
ie Moon 4 é 8 10 HID 2 4 8 70 storm. 
Ustearra -; : ; wa ; a ~; = In the accompanying illustrations, 
_ KEW HORIZONTAL FORCE 1903 { Ocr. 31, 10 21 toNOV. 1, 10 424m GMT. 
X KEW PATTERN HORIZONTAL FORCE MAGNETOGRAPH . 
Figs. 1 and 2, 1 cm. represents prac- 
tically 4 cm. of the original curves. 
SUPERINTENDENT OBSERVATORY 
DEPARTMENT. 
The National Physical Laboratory, 
Richmond, Surrey, November 7. 
Expansion Curves, 
In your issue ot October 8 Prof. John 
Perry describes in a letter “‘an ex- 
ceedingly simple, ingenious method ”’ 
of plotting the so-called polytropic 
Fic. 1.—Reduced Registeis of Horizontal Force. 
send copy of declination October 2-3, 1900, B,, Fig. 2. 
It is not absolutely quiet—very few days are, if any—and 
parts show the tiny ‘‘ magnetic waves’ often met with. 
Here, as usual, there are two days’ curves, each with its 
own base (or time) line on the same 
sheet. The paper is changed every 
second day, shortly after 10 a.m. In 
this quiet day declination curve, 1 cm. 
of ordinate in the original represents 
8/.7, and increasing ordinate answers to 
increasing westerly declination. 
The magnetic storm on October 31 
commenced about four hours before the 
papers were changed, and the assistant 
in charge, noticing that a storm was in 
progress, arranged that the papers 
should be changed again next day, so 
as to have only one day’s trace on the 
W00N 2 
sheet, and so no mixing of two days’ | a 
traces. As the commencement at ee 
6.3 a.m. is of interest, I am sending 
two sheets of the horizontal force record, 
Fig. 1, the one, A,, covering the interval 
October 29, 10.40 a.m., to October 31, 
10.16 a.m., the other, A,, October 31, 
10.21 a.m., to November 1, 10.42 a.m. 
On October 31 some of the trace is off 
the sheet about 10 a.m., also between 
2 and 4 p.m. and between 5 and 7 p.m. 
The time or base line answers to an 
arbitrary value (determined by the abso- | 
lute observations), and 1 cm. of ordinate Wee Peace ee 
in the original curve represents 507 
(where 1 y=1X10~—° C.G.S.), increasing 
ordinate representing increasing force. 
I also send a copy of part of the declination record, B,, 
Fig. 2, given by a Watson pattern magnetograph made by 
the Cambridge Instrument Company, sent to the Labor- 
atory for test. The original shows, I think, all the move- 
NO. 1777, VOL. 69] 
KEW DECLINATION 1900 { 
curve representing the law pv" =con- 
stant, which method he found in a 
pamphlet by Mr. E. J. Stoddard, of 
Detroit. I may be permitted to state that this method 
was published for the first time eighteen years ago by 
Prof. E. Brauer in the Transactions of the Society of 
German Engineers, 1885, p. 433, and since Prof. Brauer’s 
od 
f OCT.2, 1019 05,10 2646 CUT. 
» 3,10 26 10410 2AM oy 
mM. 2 4 6 é 10 
MID. 
rh 
z 
> 
s 
WATSON PATTERN DECLINOMETER MAGNETOGRAPH. 
; » ey, LO 
Fic, 2.—Reducel Registers of Declination. 
publication -this method has been used in a number 
of treatises on thermodynamics published in Germany and 
France. It has been given for years in the very valuable 
handbook ‘‘ Huette,’’ which is undoubtedly known to Prof. 
