. 
Prof. Gautier on recent Researches relating to Nebula. 107 
nebula, which was examined for many nights, presented to him 
the appearance of a hollow cylinder, seen in a direction very 
nearly parallel to its axis. Its centre, as Lord Rosse described 
it, is veiled by a curtain of nebulous matter, which is resolved 
into a thin stratum of small stars. Chacornac adds, in his com- 
munication upon this subject to Dr. Peters, under date of Paris, 
June 9th, 1862, published in No. 1868 of the ‘“Astronomische 
Nachrichten,” that when the eye is protected from all extraneous 
light the scintillation of this multitude of luminous points, oc- 
cupying a great portion of the surface of the retina, produces a 
very curious vertigo. 
- pass now to the labors of M. d’Arrest upon the nebule. 
This astronomer directed his attention to this subject while he 
Was connected with the Observatory of Leipsic, and he published 
in 1857, in the collection of memoirs of the Royal Society of 
Saxony, the results of his observations upon 230 nebule, made 
with a biannular micrometer of Fraunhofer’s construction applied 
to a telescope having an aperture of 52 lines and a focal length 
of 6 feet. Prof. d’Arrest is the acting director of the Observa- 
ty of Copenhagen, and has continued, since September, 1861, 
his observations of nebule, with an achromatic telescope of 11 
inches aperture and a focal length of 16 feet, and with a power 
estimated to be intermediate between Herschel’s 20 feet reflector 
and the telescope of the same kind with which Lassell also ob- 
Served the nebula from 1852 to 1854. The telescope of Copen- 
hagen has enabled d’ Arrest not only to recognize all the nebulze 
of Herschel, but to discover more than a hundred new ones 
objects of feeble light, with the microscopic readings of the cir- 
cles of his instrument. The result is that his new catalogue does 
them, by means of annular and wire-micrometers. It will thus be 
* 800d means of recognizing exactly their proper movements 
Searches of d’ Arrest. ‘This astronomer has published in No, 1366 
of the “ Astronomische Nachrichten” an interesting notice of his 
latest researches, dated May 20th, 1862, from which I shall ex- 
Tome details tending to complete those given above. 
Variation of the brilliancy of the nebule.—M. d’Arrest admits, 
upon the basis of the great work of Argelander who has made 
Soe catalogue of stars, that among 50,000 stars already well 
‘Own there is but a very small number whose light varies peri- 
