12 REPORT—1852. 
by an aurora borealis, the direction and appearance of the rays being very different 
from any aurora I have ever seen ; there was no change to be observed in them, and 
they kept their place with regard to the stars. At11o0’clock they had disappeared.” 
On Converging Sun-beams. Communicated by Professor PowE 1, F.R.S. 
A peculiarly brilliant instance of the phenomenon of the solar rays converging by 
the effect of perspective to a point opposite the sun immediately after sunset, was 
observed by several persons in and near Oxford, on July 6, 1852, about 8°35 P.m., 
and lasted about twenty minutes. Mr. G. A. Rowell collected the accounts of dif- 
ferent observers, illustrated by sketches, given unknown to each other, and apparently 
without their being aware of the real nature of the phenomenon. He states that— 
‘¢ All agree as to the general appearance being that of five or seven principal rays of 
bright light arising from (converging to) a point in the S.E. horizon, just opposite 
to where the sun had set. Each ray extended about 65° or 70°, and was widest at 
the upper end; the middle ray being perpendicular. There is a difference in the 
statements as to whether there were smaller rays between the principal ones....... 
The observer on Shotover Hill had a clear view of the N.W. horizon, and remarked 
that there was not at the time the slightest appearance of rays where the sun had 
gone down.” 
On the Re-concentration of the Mechanical Energy of the Universe. 
By W. J. Macquorn Rankine, C.E., PRS IE. 
Mr. Rankine observed that it has long been conjectured, and is now being esta- 
blished by experiment, that all forms of physical energy, whether visible motion, 
heat, light, magnetism, electricity, chemical action, or other forms not yet understood, 
are mutually convertible; that the total amount of physical energy in the universe 
is unchangeable, and varies merely its condition and locality, by conversion from 
one form to another, or by transference from one portion of matter to another. 
Professor William Thomson has pointed out, that in the present condition of the 
known world there is a preponderating tendency to the conversion of all the other 
forms of energy into heat, and to the equable diffusion of all heat; a tendency which 
seems to lead towards the cessation of all phenomena. 
The author of the present paper points out, that all heat tends ultimately to 
assume the radiant form; and that if the medium which surrounds the stars and 
transmits radiation between them be supposed to have bounds encircling the visible 
world, beyond which is empty space, then at these bounds the radiant heat will be 
totally reflected, and will ultimately be re-concentrated into foci; at one of which, if 
an extinct star arrives, it will be resolved into its elements, and a store of energy 
reproduced. 
On an Improved Form of Reflecting Instrument for Use at Sea. 
By Professor C. Prazzt Smytu, F.R.A.S. 
The peculiar circumstances of an observer at sea, caused chiefly by the rolling of 
the vessel, preclude the use of any of the ordinary instruments employed on land 
for measuring altitudes, depending as they do on levels or plumb lines for their zero 
points ; recourse must be had to the principle of double images by two reflectors, 
the method invented by Hadley and Newton. This one necessary principle has been 
carried out in a variety of different forms, in the sextant, quadrant, quintant or re- 
flecting circle, some more or less accurate or more or less convenient than others ; 
but all of them, under whatever names they are known, are merely different forms 
of essentially the same instrument. 
Great ingenuity has been shown in many of these forms, but still the greatest 

