70 Chronicles of Science. [Jan., 
equatorially mounted and driven by clockwork. The Astronomer 
Royal also offered to lend Major Tennant two telescopes from the 
Royal Observatory. 
As respects Photography, the conditions as to time rendered it 
unadvisable to attempt to use a speculum of more than 9} inches 
diameter. The picture will be taken at the side of the tube, the 
telescope being a Newtonian one. Provision has been made to 
obtain a field of more than one degree in diameter, so that, if 
possible, some traces of the structure of the corona may be obtained 
in the photograph. The important difference between the position 
of an equatorial used in such low latitudes as the central parts of 
India and one used in our latitudes, have rendered new designs 
necessary for almost every part of the mounting. Hence many 
unavoidable delays have taken place with respect to this part of the 
arrangements. 
Measures have also been taken to apply tests for the polarization 
of light from the coloured protuberances and the corona, the follow- 
ing three methods being applicable :— 
1st. The extinction of the polarized portion of the light by 
means of a Nicol’s prism, reducing the intensity of the image to a 
minimum. 
2nd. Savart’s test, where parallel fringes are formed by the 
interference of the polarized rays, the central one being either 
dark or light, as its plane is in or perpendicular to the plane of 
polarization. 
3rd. By a double-image prism and analyzing plate, giving 
images of complementary colours with polarized light. 
The first two of these tests can be instantaneously interchanged, 
and there is no difficulty in using all these tests successively in two 
minutes, 
For spectrum observations, the Astronomer Royal has lent Major 
Tennant one of the old collimators of the Transit-Circle at Green- 
wich Observatory. An equatorial mounting is bemg constructed 
for this, to follow any object steadily, but without clockwork. The 
spectroscope will allow of the spectrum being compared with a scale 
of equal parts, by means of which its peculiarities can be referred to 
the limes of the solar spectrum. 
All the estimates for the expenses of the proposed operations 
have been duly sanctioned. 
Mr. Proctor gives the elements of his new determination of the 
Rotation-period of the planet Mars. A comparison of pictures 
taken by Mr. Browning in February of the present year with 
Hooke’s observations in March, 1666—giving a period of nearly 
two hundred and one years—have enabled Mr. Proctor slightly to 
correct his former estimate—in obtaining which one or two small 
errors had crept in. He now gives for Mars’ sidereal day the 
