1865.] Astronomy. 653 



and other observers as to the relation in which sun spots stand to the 

 planets. In 1859, when he sought by means of a formula dependent 

 on tbe periods and masses of the four planets Venus, Earth, Jupiter, 

 and Saturn, to represent a curve analogous to the sun-spot curve, he 

 stated that Jupiter determines the leading character of the Sun-spot 

 curve, that Saturn causes small alterations in the height and length 

 of the undulations, and that the Earth and Venus determine the inden- 

 tations of the curve. 



As subsequent observers have drawn attention to the connection 

 between sun-spots and planets, especially Jupiter and Venus, Professor 

 Wolf has in this paper given some statements as to the connection 

 between the sun-spot period and the revolution of Jupiter. A table 

 is given in w T hich it is seen that the period 11-11 completely satisfies 

 what is only to be expected from a mean period affected with the con- 

 siderable oscillation, 1 • 75 ; and not only there corresponds to the 

 mean course thereof a good wave line with the difference, 42*96, 

 between maximum and minimum, but the single maxima and minima 

 accord well together, with only a slight displacement of the minimum 

 of 1783 and the maximum of 1786. 



A new arrangement of two solar prisms for use with a micro- 

 meter has been described by the Reverend W. R. Dawes. The 

 transparent glass diagonal, suggested by Sir J. Herschel, is a very 

 valuable adjunct in observations where it is desired to determine the 

 relative situations of solar spots by means of a micrometer, as it 

 permits a large aperture to be employed without danger to the dark 

 glasses. But a very considerable difficulty arises from the fact that 

 the relative positions of the spots and of the points of the compass, 

 as thus seen, are different from their positions as they appear in the 

 astronomical refractor. To # remedy this inconvenience, Mr. Dawes 

 has been in the habit of combining two pieces, each of which had a 

 transparent glass diagonal, capable of being used separately or to- 

 gether. By this simple contrivance the image as reflected from both 

 the combined prisms is seen in the direction of the axis of the 

 telescope, and its various parts are in the same relative positions as 

 when no diagonal is used. 



At the June meeting of the Society, Mr. Dawes also gave a paper 

 on the planet Mars, in which numerous curious and interesting 

 features were described, such as the long, narrow strait, running N.E. 

 and S.W. in the northern hemisphere ; an oval bay with a regular 

 coast, in which lately a distinctly forked appearance was noticed, 

 giving the impression of two very wide mouths of a river which, 

 however, he could never trace. Speaking of the colour, the author 

 considers that nothing can more fully prove that the ruddy tint of 

 Mars does not arise from any peculiarity in the colour of the planet's 

 atmosphere, than the fact that the redness is always deepest near the 

 centre, where the atmospheric stratum is thinnest ; while near the 

 edge of the planet the grey features are obscured, and in general 

 entirely hidden, by the density of the atmosphere, and yet the colour 



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