Miscellaneous ene. 431 
4. Third Comet of 1853, (Atheneum, Sept. 17. \—The comet ve 
was so conspicuous near the western horizon about the first of Septem 
ber, reached its greatest brilliancy on the 8d of Sept.; on which da 
shortly before one o’clock, Pp. M., the nucleus was perceived in full day: 
light by Mr. Harrnup, of the Liverpool Observatory. It appeared 
round, and about 9” in diameter, without any appearance of a tail. 
. Sho 
servations reported in oe last number of this Journal, the following 
ave been received, . Coulvier Gravier, at Paris, reports (Comptes 
Rendus, tom. 37, p. 288) the hourly number on the 9th at 49, and on 
the 10th, 56, but omits to give the number = observers, and ‘the time 
of night in which his observations were ma 
Rev. Andrew T. Pratt, M.D., Missionary of the American — at 
Aintab, Turkey, has communicated some observations made by mself 
and another person Aug. 9-1lth. The evenings were Piles 2 but 
their view was confined to the part of the heavens west of the meridian, 
and above the altitude of twenty degrees 
n the 9-10ih, from 9 to 10 0 ‘lode “they saw 36, and from 1 to 2 
Fre ea 66. On the 10-IIth, from 12 to 1 o’clock they saw 78, and 
from 1 to 2 o’clock, 88. The general tection of the meteors was 
quite sig the radiant being near Cassio 
hese observations agree with those ceaceton made at New Haven 
as to sl ener direction and greater frequency after midnight, 
and confirm, what erhaps be considered as sufficiently well estab- 
lished, the etal a of shooting stars. 
VI. MisceLuaneous INTELLIGENCE. 
1. Note to Prof. righ paper on ep agp of Heat in the 
Hot-air Engine, page 351; by the Aurnor.—In Appleton’s Mechan- 
ic’s Magazine for Ae dtneel is editorially stated, on the authority of 
Capt. Ericsson, that the engines now in preparation for the caloric ship 
are to have working cylinders of 6 feet diameter and 8 feet stroke, are 
to be double-acting, and are to draw their supplies from a reservoir of 
highly condensed air kept artificially cold, to which the escaping air is 
to be returned. This construction requires no modification of the theory 
of the engine, but renders necessary, in the gen neral formula, the sub- 
perdi : 15142, or as 54:49. The stroke, being also increased in 
the ratio 4: 3, will i increase dis nominal horse-power, should the same 
number of revolutions be maintained, in the same ratio. The powers 
given in this table, therefore, being multiplied ak:  aoxa= Z will give 
the gore ere powers of the new engine 
tion of economy, however, remains unaffected, since the 
mass air se be heated is increased in precisely the same ratio as the 
power. The mass varies as the product of volume into density ; 
