271 



Much, however, in Mr. Pepys's estimation, remained to be done in 

 the mechanical part of the apparatus, and in the course of various 

 experiments on these subjects, that it might be rendered more com- 

 modious in its application, and capable of giving correct results with 

 the utmost minuteness. 



The instruments which he proposes consist of two tubes, one larger 

 and one smaller, with a bottle of elastic gum to each, and a glass cy- 

 linder, or cistern, of the same length as the tubes. The larger of the 

 tubes, containing one cubic inch, is the principal measure, and is di- 

 vided into hundredths ; the smaller is intended to measure fractional 

 parts ; and in this each of the former divisions is divided into ten 

 parts, or thousandths of the cubic inch. 



One of the bottles of elastic gum has attached to it a tube, which 

 serves as a perforated stopper to the larger measure, through which 

 any liquid to be applied to the gas under examination may be for- 

 cibly injected. When the full contraction has taken place, the mea- 

 sure is immersed in the cistern, filled with mercury or with water, 

 according to circumstances, and the contraction noted. But if the 

 surface is found not to correspond with a division of the principal 

 measure, the smaller tube, which slides through a cork in the bottom 

 of the cistern,-' is to be passed up till its extremity (which is open) 

 reaches the gas contained, and the fractional part is then withdrawn 

 by means of its elastic bottle, and measured with the greatest pre- 

 cision. 



Mr. Pepys next proceeds to an account of various gases, .of which 

 he tried the purity by means of this apparatus, as nitrous gas, con- 

 taining -r-J-ihr of impurity, oxygen gas -r^ ; atmospheric air, of which 

 iVuV were absorbed ; carbonic gas, which left i-J-o-jand sulphuretted 

 hydrogen T -tfW of impurity. 



In the analysis of compound gases also, he imagines it will be found 

 peculiarly useful. He recommends using the solutions hot, which 

 facilitates chemical union, but prevents the absorption of carbonic 

 and other gases by the mere water of solution, which might other- 

 wise take place. 



In order to uvoid the expansion that would be occasioned by 

 handling the measure, Mr. Pepys employs a pair of forceps, having 

 circular extremities lined with cloth, for grasping the tube. 



The elastic gum, he observes, is so little acted upon by chemical 

 agents, that a great variety of them may be employed, and may with 

 facility be used at any temperature. 



Observations on the Nature of the new celestial Body discovered by 

 Dr. Olbers, and of the Comet which was expected to appear last 

 " January in its return from the Sun. By William Herschel, LL.D. 

 F.R.S. Read June 4, 1807. [Phil Trans. 1807, p. 260.] 



It was on the 24th of April that Dr. Herschel first saw the new 

 planet Vesta ; but though he saw her again on the 25th, he could 

 not determine which of several stars he noted was the planet, for 



