SCIENTIFIC SUMMARY 
ASTRONOMY. 
yi NEW Driving -clock for Equatorials . — Lord Lindsay and Mr. David 
Gill liave described to the Astronomical Society a form of clock which 
they have devised, and which bids fair to render the higher accuracy of rate 
which is now demanded by spectrum analysis and celestial photography 
readily attainable. The following conditions have been endeavoured to 
be realised : — 
1. A driving power four or five times as great as that actually required, 
so as to avoid failure when the balancing of the instrument is defective. 
2. A rate of motion equal in accuracy to that of a good sidereal clock. 
3. Maintenance of the same uniformity of rate under change of work to 
be done, twice as great as that to which the clock will be likely to be 
submitted. 
4. An easy and rapid means of adjusting that rate, and so avoiding delay 
in timing as much as possible. 
The methods by which these several conditions have been arrived at, 
detailed in full, with various illustrations explaining the machinery em- 
ployed, were given at the Proceedings R.A.S. 
New Observations on Presence of Magnesium at the Edge of the Sun . — 
M. Tacchini gives observations, from June to end of August, of magnesium, 
line b , and the line 1474 k, the number of positions each day being noted. 
These vary from 26 to 60. August shows a maximum. The line 1474 k 
is always found where the line b is found ; but the reverse does not always 
occur. Against M. Faye’s theory the writer points out, among other things, 
that the penumbrse of spots are generally very broad, and many of their 
tongues, or currents, go to the very bottom in a way contrary to that which 
cyclones would show. — See “ Comptes Rendus,” Sept. 8. 
On Aurorce Boreales. — A very important and valuable paper is that laid 
before the French Academy lately by M. Faye. Donati, he says, seeks the 
explanation of auroras in a meteorology which he terms cosmic. The phe- 
nomena are probably due to electro-magnetic currents going from the sun 
to the planets, their vehicle being ether. He himself hesitates to accept 
this view, and directs attention to the forces really acting in interplanetary 
space. In addition to attraction there is the force producing the phe- 
nomena of comets. Might not this, operating on our earth, give rise to 
auroras P The effects of this repulsive force are proportioned by surfaces and 
not by masses. Insensible in very dense bodies, they become enormous in 
