514 
NATURE 
[April 27, 1871 

Hence, for the centre of the earth, 
- doh m s 
° 
First external ‘contact ... June 5 10 22 Ir at 49°3 
from N. towards E. ° . " p a ‘ 
First internal contact ... June § 10 39 at 37°8 
from N. towards EE.  . ‘ 3 ; ; a i oe 
Secondinternalcontact ... June 5 16 42 6at2g31 37° 
from N. towards E. q 2 - ‘ slew SS 2 
Second externalcontact ... June 5 17 0 Oat 290°5 
from N. towards E.  . , . 5 . - 
And, with the same notation as before, I find for the reduction 
for parallax, 
Ist ext. cont. =June 5d roh 22m 11s +[2°4536] p .sin 7—[2*4582] 
-p-cos/, cos(A+412 28’). 
Ist int, cont. =June 511 roh 39m 56s +[2°4838] p .sin 7— [2°4558[, 
-p. cos /, cos(A+43° 52’). 
211 int. cont. =June 5d 16h 42m 63—[2"1301] p .sin 7+[2°5968] 
. p. cos Z, cos(A—10° 57’). 
2nd ext. cont. =June 5d 17h om Os —[2°1158] p.sin 7+[2°5825] 
- pcos Z, cos(A— 6° 28’), 
At Greenwich the egress only will be visible. 
d hom s 
Last internal contact June 5 at 16 44 23 | Mean times at 
», external ,, », ati7 2 15) Greenwich. 
The sun will rise at 15h 46m. 
J. R. Hinp 


AMERICAN NOTES 
“THE year 1871 bids fair to be marked in the history of 
American science for the great number of exploring expe- 
ditions under the auspices of the United States Government. 
First, that of Captain C. F.. Hall, the well-known Arctic travel- 
ler, for whose proposed Polar Exploration the United States 
steamer Periwinkle is now being prepared at the Washington 
Navy-yard. This vessel, of nearly four hundred tons burden, 
is said to be very.staunch and reliable, and her equipment will 
be of the best order. It is understood that the expedition will 
start about the end of May, and that Captain Hall’s scientific 
assistants will be Dr. David Walker, formerly known as the 
surgeon and physicist of Sir Leopold M‘Clintock’s expedition in 
the Fox, and Dr. Emil Bessels, who has seen Arctic service in a 
Spitzbergen expedition. Dr. F. V. Hayden, long known to the 
public as a geologist and explorer, continues his labours of the 
past season, with the aid of an appropriation by Congress of 
40,000 dols, His party is now being fitted out, and will be pro- 
vided with the necessary assistants in all branches of research. 
His work will be to the northward of the scene of his last 
year’s explorations. A third expedition is that of Lieu- 
tenant G. M. Wheeler, which, under the direction of the War 
Department, proceeds to explore certain little-known regions of 
Arizona and Southern Nevada, including the country about the 
Lower Colorado and Bill Williams Fork. This work will require 
several years for its completion. Lastly, Major Powell continues 
his labours during the present season, and expects to make a 
careful examination of the Canons of Green River as well as of 
the Colorado.—Attention was called some time ago to the high 
scientific value of the collection of objects made by the late Dr. 
Klemm, of Dresden, for use in his “ History of the Progress of 
Human Civilisation ;” and it was suggested that in its great ex- 
tent, and in the harmonious exhibition of illustrations of human 
art and handicraft in every department, it would constitute an 
important addition to the means of instruction in the city of 
New York. An association of parties in Leipsic has accom- 
plished its purchase, at a cost of over ten thousand dollars ; and 
has determined to make it the basis of an international anthropo- 
logical museum, which, it is expected, will be one of the most 
complete in the world. Contributions from all parts of the globe, 
and especially from America, are invited by the committee having 
the matterin charge, and we trust that the appeal will not be in vain. 
—Stimulated by the success of the experiment made by the Phiia- 
delphians in stocking the Delaware River with black bass, some 
public-spirited gentlemen of Reading, Pennsylvania, have under- 
taken to try the same experiment in the Schuylkill, and 350 
dollars have already been subscribed for that purpose.—The 
town of Amherst, in Massachusetts, has followed the example of 

New York, Philadelphia, Boston, and other places, in intro- 
ducing English sparrows, in the hope of establishing a colony of 
these birds.—The San Francisco papers are calling attention to 
specimens of fossil ivory brought from Alaska ; and parties are 
said to be about entering upon the business of collecting it on a 
large scale. This ivory consists of the tusks of the mammoth 
or fossil elephant (Zvephas primigenius), the remains of which 
are extremely abundant in Alaska, but much more soin Siberia, 
from which latter country, as is well known, an appreciable per- 
centage of all the ivory now used in the arts is obtained.—The 
College of the City of New York in Twenty-third Street, shows 
a commendable desire to increase its means of instruction in ~ 
natural history, and particularly in the department of osteology, 
the president having succeeded by unremitting effort in obtainin, 
means to secure quite a large number of specimens, among whic 
may be especially mentioned a large slab of stone containing a 
well-preserved skeleton of the /chthyosaurus, or fish-like fossil 
lizard from the Lias of Germany. The specimen is about ten 
feet long, and, from its perfection and excellence of preseryation, 
is justly entitled to consideration. 
EXPERIMENTS ON THE SUCCESSIVE POLA- 
RISATION OF LIGHT, WITH DESCRIPTION 
OF A NEW POLARISING APPARATUS * 
THE term successive polarisation was applied by Biot to 
denote the effects produced when a ray ae polarised light is 
transmitted through a plate of rock-crystal cut perpendicularly 
to the axis, or through limited depths of certain liquids. In 
these cases the plane of polarisation is found to be changed on 
emergence, and differently for each homogeneous ray, so that, 
| when white light is employed, on turning the analyser round 
continuously in one direction different colours successively 
appear, rising or falling in the scale according to the nature of 
the substance. 
If, while the analyser is turned from left to right, the tints 
ascend (2.2. follow the order R, O, Y, G, B, P, V), the sub- 
stance is said to exhibit right-handed successive polarisation, but 
if the tints descend, the successive polarisation is said to be left- 
handed, 
These phenomena were satisfactorily explained by Fresnel in 
the following way. The incident polarised ray, instead of re- 
solving itself into two plane polarised rays at right angles to each 
other, as in the ordinary cases of dipolarisation, resolves itself 
in these instances into two circularly polarised rays, one right- 
handed the other left-handed, which are transmitted with different 
velocities ; each homogeneous ray, thus resolved into two opposite 
circularly polarised pencils, on emergence composes a ray polar- 
ised in a single plane, the deviation of which from the primitive 
plane of polarisation depends on the difference of phase of the 
two circularly polarised rays on emergence. 
The rotation of the planes of polarisation is from left to right 
or from right to left, according to whether the right-handed or 
left-handed circular rays are transmitted with the greater velocity. 
The term dipolarisation, proposed by Dr, Whewell to express 
the bifurcation which a ray of polarised light suffers when it is 
transmitted through a crystallised plate, is a very appropriate 
one ; but asthere are different kinds of such separation, we may 
designate plane dipolarisation the resolution into two plane- 
polarised rays at right angles to each other, and circular dipolari- 
sation the resolution into two circularly polarised rays, one right- 
handed the other left-handed. In like manner the term elliptic 
dipolarisation may be employed to represent the phenomena 
shown by transmitting a polarised ray through a plate of rock- 
crystal obliquely to the axis. 
The object of the present communication is to make known 
another means of producing successive polarisation, both right- 
handed and left-handed, which, equally with the well-known 
modes, may be proved to arise from the interference of two 
opposite systems of circularly polarised rays. 
The polarising apparatus which I have employed for the ex- 
periments I am about to detail is represented by Fig. 1. 
A plate of black glass, G, is fixed at an angle of 3° to the 
horizon. The film to be examined is to be placed ona diaphragm, 
D, so that the light reflected at the polarisinglangle from the 
glass plate shall pass through it at right angles, and after reflec- 
tion at an angle of 18° from the surface of a polished silver 
* From the Proceedings of the Royal Society, 
