101 



increasing series of gauging powers, by which the profundity in space 

 of every object consisting of stars can be ascertained, as far as the 

 light of the instrument will reach, Sir William Herschel proceeds to 

 make use of some of his numerous observations made upon those oc- 

 casions, to show how the distances of globular and other clusters of 

 stars may be obtained, and has represented their situations in space 

 by a figure, in which their distances are made proportional to the 

 diameter of a globular space, sufficiently large to contain all the stars 

 that are visible to the eye of an observer in the clearest nights. 



The author then details a series of observations of clusters of stars, 

 from which the order of their profundity in space is determined, and 

 describes the manner in which he represents the profundity of celes- 

 tial objects in space by diagrams ; and in the concluding section of 

 his paper, considers the extent of the power of telescopes to reach 

 into space when they are directed to ambiguous celestial objects. 



On the Structure of the Poisonous Fangs of Serpents. By Thomas 

 Smith, Esq. F.R.S. Read June 4, 1818. [Phil. Trans. 1818, 

 p. 471.] 



The object of this paper is to explain the existence of a slit in the 

 fangs of serpents, extending from the foramen at the base to the aper- 

 ture near the point, and to show that this slit is caused by the manner 

 in which the tube through which the poison flows is formed. After 

 describing the growth oif the teeth of poisonous serpents, the author 

 observes, that in those which are not venomous, there are no traces 

 of any furrow or depression. 



A drawing, illustrating the author's description, is annexed to this 

 paper. 



On the Parallax of a Aquilce. By John Pond, F.R.S. Astronomer 

 Royal. Read April 16, 1818. [Phil. Trans. 1818,^. 477.] 



The telescope erected for this investigation resembles in its con- 

 struction that which was formerly used . for the observations of 

 a Cygni. It has an achromatic object-glass of 10 feet focal length, 

 and 4 inches diameter. 



The Astronomer Royal had first selected ft Canis Minoris as a 

 proper star to be compared with a Aquilse ; but finding, upon trial, 

 that it could rarely be seen in the day-time, he was induced to sub- 

 stitute X Pegasi. Not being quite satisfied of the stability of the in- 

 strument, the author has only computed those observations in which 

 each star was observed in the same day, and in the short interval of 

 three hours ; so that it was not likely any sensible change in the te- 

 lescope should have taken place. The result of fifty-four observations 

 between the 25th of July and the 29th of December 1817, afforded 

 no appearance of parallax ; indeed the author considering it as a 

 hopeless task to establish its existence by observations on a star so 

 far from the zenith, was about to abandon the subject, when his at- 



