SEPTEMBER 25, 1913]| 
NATURE 
97 
_In the appendix to Captain Parry’s *‘ Arctic Voyage, 
1821-3,’’ p. 187, some observations of the sea horizon 
by Mr. Fisher are given. He found a variation of 
18° in the Arctic region, the ice horizon being ele- 
vated in summer and depressed in winter. The 
variation of the place of the apparent horizon, as a 
question of unequal temperature, was discussed 
generally by M. Biot in 1809. But no detailed 
observations on the subject have, so far as 1 am aware, 
been yet made. 
The correction for refraction in obtaining the heights 
of mountains by angles of depression to the water- 
line of points or lighthouses, or by angles of elevation 
from points the height of which has been ascertained, 
is taken empirically, in nautical surveying, as 5th 
the distance of the object observed. The results thus | 
obtained are fairly accurate. For instance, when sur- | 
veying the Gulf of Suez in 1871, the observaticns from 
the summit of Jebel Hooswah gave the results shown | 
in the accompanying table. 
stalled. It may be mentioned that a trial instrument 
was made for the International Seismological Associa- 
tion by the Cambridge Instrument Company, and 
installed on the pier at Newcastle-on-lyne. It did 
its work, but the position is not suitable for the pur- 
poses of correlation. The west coast of Ireland or 
of Norway would have been better. However, prac- 
tical difficulties stood in the way for utilising either 
for the trial instrument. The present instrument, 
made by the same company, has been improved on 
the former, but has as yet no contrivance for regis- 
tering the height or magnitude of the waves, which 
is so very desirable. 
The principle of the instrument is very simple. It 
is based on Boyle’s law, PV =constant. An iron pipe 
—in our case 625 ft. long—is led from the instrument, 
the diaphragm part, to and into the ocean to a depth 
beneath the trough of the assumed highest waves at 
low tide, say 15 ft. The sea-end of the pipe is open. 
The wave passing over it causes the water to rise in 
T. H., Tizarp. the pipe and compress the air beyond, whereby the 
s¢ : | Height of Corrected height 
Pas i iff. aN eat 
Place of observation Object observed ae Henicens res Bese Dist. vol Bt Dip. Pl | Ob 
=F Fea tier. Vv 5 | ace ject 
<9 pet mut ts observed Theod. Serres Wetec 
Summit of Jebel | Water line of Tur point...) — | 1 27 30. +1 21 | 1 28 51| 16°38 |2573, Oo 5 ft. | 237) 2331 ° 
Hooswah ; 50 at Tur ... }—]1 20 0 +1 31 | 1 21 31) 18°24 |2633 ° mr 292, 2336 ° 
=F Marabut point | — | 3 57. 0, +0 27 | 3 57 27| 5°48 |2303 o a 26) 2272 fo) 
ae point this side | 
of Marabut;... eeoeiest| — 4) I 0, +0 26 | 4 1 26) 5°35 |228- fo) 3 24 2258 ° 
Watcr line to the right .... — | 4 49 0, +0 23] 4 49 23) 4°60|2358 0 a 19, 2334 fo) 
ve ofstation point — |16 12 0 +0 6 |16 12 6) 1°30 |2295 ° - 1) 2289 fo) 
ay of another 
point with station —|11 18 0 +0 9g |11 18 9] 1°85 2246, Oo =3 3) 2238 fo) 
Water line of another point, — | 8 54 40) +0 12 | 8 54 52| 2'40|2287, Oo on 5| 2277 fo) 
me by Asses ears. — 1614 0 +017 | 6 14 17| 3°48 |2311 fo) - Il. 2295 ° 
Mean height 2292 ft. Max. height observations 2336. Minimum 2238. Range 98 ft. 
For greater distances and heights the angles from and to Jebel Serbal may be given as follows :— 
Summit of Jebel | Water line of Gharib light- | | 
Serbal Hiouse: ©...! lscsliasaianees | —|2 6 of +2 47/2 8 47 33°48 |7623 0 “ 989 6629 fo) 
| Water line of Zaffarana | 
lighthouse see eve | — | I 28 9, +4 53 | I 32 53) 58°55 9613 sx (3025) 6583 ° 
| Point to south-east of Zaf- | | | 
farana lighthouse — | 225 0} +2 24 | 2 27 23) 28°9 |7533 0 »» | 737) 679% ° 
Abu Zenina point ... —]|158 of +3:07/]2 1 73773317994 Oo >» 1230) 6758 ° 
Water line Tur Spit ...| — | 2 42 ) +2 4] 2 44 4 zqrgoli7225; 0 | ,, 551) 6699 fo) 
Summit of Jebel Hooswah | — | 2 30 0} +1 29 | 2 31 29,17°92 4801 2292 ,, 285) 6803 | 2292 
Mean height 6706 ft. Max. 6803. Min. 6583. Extreme range 220 ft. 
The Undagraph. 
Last week the Dominion Astronomical Observatory 
installed at Chebucto, near Halifax, Nova Scotia, a 
wave-counter, which I have called an ‘undagraph.” | 
The site, a granite cliff 110 ft. high, on which is a | 
lighthouse, faces the broad waters of the Atlantic. 
The coast hereabouts is bold and rocky. 
Modern seismographs record tremors of the earth— 
microseisms—not attributable to earthquakes, and in- 
vestigators have traced them to the action of the 
sea during storms. These microseisms manifest 
themseives particularly markedly in Ottawa and in 
Europe from autumn to spring, ?.c. during the winter 
or stormy season. Their period ranges, say, from 
four to seven seconds, and the greater the storm or 
steeper the gradient of the ‘“‘low”’ on the water along 
the coast, the greater is the amplitude of the micro- 
seisms. : 
In order to correlate the period of the waves of the 
ocean which pound upon the coast with the period of 
the microsiesms, the above instrument has been in- 
NO. 2291, VOL. 92] 
leather diaphragm is raised, and electric contact is 
made. By means of the armature of an electro- 
magnet a toothed wheel is pushed forward, one 
tooth for every wave, and with one revolution, or 
120 waves, the recording pen returns to its zero. 
The record presents a series of finely serrated oblique 
lines, each representing 120 waves. Clockwork with 
pen traces at the edge of the paper a time scale, 
making a break every hour, the linear measure of which 
is 6cm. A fresh roll of paper is put on once a week. 
A small leak is provided in the diaphragm chamber, 
to cut out the effect of the slowly rising and ebbing 
tide, which, however, does not affect the rapid action 
| by the waves. 
The sea-end of the pipe gives the most anxiety, as 
it has to resist the immense force of the waves during 
storms. The greater part of the 625 ft. is of half-inch 
galvanised iron pipe, while the ocean end, about 
too ft., is of four-inch pipe, with reducing pipes be- 
tween the preceding two. The bedding of the sub- 
merged part will be in about four tons of concrete 
