76 



is described by Sir Everard Home. The ova are deposited upon its 

 own shell ; sometimes one only, sometimes several, contained in one 

 chamber. 



The animal found in the Argonaut shell by Mr. Cranch, had de- 

 posited eggs upon the lip of the shell ; they were united by pedicles, 

 like those of the Sepia octopus, and differed from those of the Helix 

 ianthina, and other testaceous Vermes living in water, in having no 

 camerated nidus, and in having a very large yolk to supply nourish- 

 ment to the young animal when hatched ; so that this animal, says 

 Sir Everard Home, must be resolved into a species of Sepia ; an 

 animal which has no external shell, and which only uses the Argo- 

 naut when it occasionally gets possession of one. 



Some naturalists not acquainted with comparative anatomy have 

 thought they saw the Argonauta shell partly formed in these ova. 

 The appearance they allude to is probably the unusually large yolk. 



Astronomical Observations and Experiments tending to investigate the 

 local Arrangement of the Celestial Bodies in Space, and to determine 

 the Extent and Condition of the Milky Way. By Sir William Her- 

 schel, Knt. Guelp. LL.D. F.R.S. Read June 19, 1817. [Phil. 

 Trans. 1817,^.302.] 



The construction of the heavens, in which the real place of every 

 celestial object in space is to be determined, can only be delineated 

 with precision when we have the situation of each heavenly body 

 assigned in three dimensions, which, says the author, in the case of 

 the visible universe, may be called longitude, latitude, and profun- 

 dity. The angular positions of the stars given in astronomical cata- 

 logues, and on globes and maps, may enable us to find them by the 

 eye or telescope; but their distance remains unknown; and unless a 

 proper method for obtaining the profundity of objects can be found, 

 their longitude and latitude will not enable us to assign their local 

 arrangement in space. The method of parallaxes has succeeded 

 with regard to objects comparatively near. The parallax of the 

 fixed stars has also been an object of attention ; and although the 

 investigation has hitherto produced nothing satisfactory, it has given 

 us a magnificent idea of the vast extent of the sidereal heavens, by 

 showing that probably the whole diameter of the earth's orbit, at the 

 distance of a star of the first magnitude, does not subtend an angle 

 of more than a single second of a degree. To stars of a smaller 

 size the parallactic method admits of no application. 



Sir William Herschel proceeds to consider the local situations of 

 the stars, and proposes a standard by which their relative arrange- 

 ment may be examined ; that is, by comparing their distribution to 

 a certain properly modified equality of scattering, in which it is not 

 required either that the stars should be equidistant from each other, 

 or that those of the same nominal magnitude should be equally 

 distant from us. A certain equal portion of space is allotted to every 

 star, so that we may thus calculate how many stars any given ex- 



