1868. | Mathematical and Physical Science. 518 
of aspect by varying angles of illumination and changes dependent 
upon libration. It will at once take a standing at least equal to 
those branches of astronomy which have been of late years par- 
ticularly fruitful in discovery. 
The Report entered somewhat largely into the question of 
change on the moon’s surface, which is still undecided. The un- 
certainty as to the accuracy of former delineations and records 
combined with the extraordinary changes which some objects 
undergo—changes not altogether new, as they have been observed 
previously by Schréotter—render it very difficult to decide as to 
whether any real change has taken place. 
This Report was followed by two papers on an allied subject 
viz. by Baron Von Madler “On Changes of the Moon’s Surface ;” and, 
W. Rt. Birt, Esq., “On the Extent of Evidence of Change on the 
Moon’s Surface.” Father Secchi then gave an elaborate account of 
his “ Researches on Spectral Analysis of the Stars.” Mr. W. F. 
Barrett gave two papers “On the Passage of Radiant Heat through 
Liquids,” and “Ona Simple Method of Exhibiting the Combination 
of Rectangular Vibrations.” 
On Friday the 21st, the first paper read was “On a Further 
Development of the Dynamo-Magneto-Electric Machine,” by W. 
Ladd. In this machine the continuity of the electric current 
depends upon the armatures revolving with a rapidity of from 1,800 
to 2,000 revolutions per minute; but as the armatures have to be 
magnetized and demagnetized twice during each revolution, there 
would be in the latter case 4,000 flashes of ight per minute. Now, 
it has been shown that every time iron becomes magnetized it is 
elongated, and again shortened when demagnetized. At every 
alteration, therefore, of the condition of the iron some small amount 
of heat must be devolved, and would increase to such an extent 
that, if unchecked, it would in course of time be so great as to 
destroy the insulation of the wire. To obviate this Mr. Ladd has 
perforated the two poles of the electro-magnet as close as possible 
to the armatures, and a stream of cold water circulates twice round 
the machine. This carries off the heat in a most effective manner, 
and no appreciable detriment in its electrical results occurs. 
In the discussion which followed, Mr. Ladd said he wished to 
make a remark or two about the heating of the armature. He did 
not wish it to be inferred that the sole cause of heat was the elonga- 
tion of the iron. Doubtless the electric currents passing through 
the wire would produce heat; but he believed that the quantity of 
heat produced by that means was small as compared with that pro- 
duced by the elongation of the iron itself. He entertained this 
opinion for the following reason. He had lately applied one of 
these magneto-machines, driven by steam-power, in connection with 
a large inductorium, giving about 18-inch sparks; and ie a few 
2N 
