212 



NATURE 



[June 30, 1892 



a Boer republic has been declared in the plateau region of 

 Angola, one of the healthiest parts of tropical Africa. 



The survey of the district surrounding Aden has been com- 

 pleted by the officers of the Survey of India Department 

 after a very arduous campaign. Work was on several 

 occasions almost stopped by sickness, and by the open hostility 

 of the natives. 



Stimulated by the recent discovery of two complete 

 mammoth carcases in the Government of Irkutsk, the St. Peters- 

 burg Academy of Sciences has commissioned Prof Tcherski, of 

 Irkutsk, to proceed to Yakutsk, on the Lena, and thence, 

 accompanied by Cossacks and pack-horses, eastward to the 

 Kolyma Valley, pushing on if possible this summer to Nizhne 

 Kolymsk in 69° N., returning before winter to Sachiversk on 

 the Indigirka, a town situated on the Arctic Circle. The 

 .nain object of the expedition is to study the drift geology, but 

 collections will be made in all departments of science, including 

 barometric observations, in order to determine the orography 

 of this rarely visited part of Siberia. 



Globus announces the formation of a new islet in the Caspian, 

 near Baku, by upheaval. It lies three and a half miles from 

 shore, and measures 175 feet by 100 feet, rising about 20 feet 

 above the water. Its surface is irregular, and composed of 

 blackish -grey and yellow hardened mud. 



With reference to the note on p. 65 as to the discovery of a 

 new range of mountains in Benin, it is only fair to former 

 travellers in that region to say that the map by the Intelligence 

 Department, although bearing no mountain shading, has marked 

 upon it " Mt. Ara," very near the position where the range seen 

 by Governor Carter is situated. 



The mountaineering expedition, led by Mr. Conway, to 

 attempt the ascent of the loftiest Himalayan summits, has been 

 making excursions from Gilgit and mapping the Bagrot Valley, 

 but bad weather has prevented any very important climbing from 

 being done. A Times telegram from Calcutta conveys news of 

 June 8 from Gilgit, from which it appears that the greatest height 

 yet reached is 17,000 feet, one night having been passed at an 

 elevation of 15,600 feet. The party was about to set out for 

 Nagar, en route for Askoley, by the Hissar Pass. 



A NEW FORM OF AIR LEYDEN. 1 



TN the title of this paper as originally offered for communica 

 ■^ tion " ^jV Condenser'" %Xoo^'vci place of ^^ Air Ley den,' 

 but it was accompanied by a request to the Secretaries to 

 help me to a better designation than " Air Condenser " (with its 

 ambiguous suggestion of an apparatus for condensing air), and I 

 was happily answered by Lord Rayleigh with a proposal to use 

 the word " leyden " to denote a generalized Leyden jar, which 

 I have gladly adopted. 



The apparatus to be described affords, in conjunction with a 

 suitable electrometer, a convenient means of quickly measuring 

 small electrostatic capacities, such as those of short lengths of 

 cable. 



The instrument is formed by two mutually insulated metallic 

 pieces, which we shall call A and B, constituting the two sys- 

 tems of an air condenser, or, as we shall now call it, an air 

 leyden. The systems are composed of parallel plates, each set 

 bound together by four long metal bolts. The two extreme 

 plates of set A are circles of much thicker metal than the rest, which 

 are all squares of thin sheet brass. The set B are all squares, 

 the bottom of which is of much thicker metal than the others, 

 and the plates of this system are one less in number than the 

 plates of system A. The four bolts binding together the plates 

 of each system pass through well-fitted holes in the corners of 

 the squares ; and the distance from plate to plate of the same set 

 is regulated by annular distance pieces which are carefully made 

 to fit the bolt, and are made exactly the same in all respects. 

 Each system is bound firmly together by screwing home nuts on 

 the ends of the bolts, and thus the parallelism and rigidity of the 

 entire set is secured. 



The two systems are made up together, so that every plate of 

 B is between two plates of A, and every plate of A, except the 

 two end ones, which only present one face to those of the op- 



1 "On a New Form of Air Leyden, with Application to the Measurement 

 of Small Electrobtatic Capacities." Cy Lord Kelvin, P.R.S. Kead at the 

 Royal Society on June 2. 



posite set, is between two plates of B. When the instrument is 

 set up for use, the system B rests by means of the well-known 

 " hole slot and plane arrangement,"^ engraved on the under 

 side of its bottom plate, on three glass columns which are 

 attached to three metal screws working through the sole plate of 

 system A. These screws can be raised or lowered at pleasure, 

 and by means of a gauge the plates of system B can be adjusted 

 to exactly midway between and parallel to the plates of system 



A. The complete leyden stands upon three vulcanite feet at- 

 tached to the lower side of the sole plate of system A . 



In order that the instrument may not be injured in carriage, 

 an arrangement, described as follows, is provided, by which sys- 

 tem B can be lifted from off the three glass columns and firmly 

 clamped to the top and bottom plates of system A. 



The bolts fixing the corners of the plates of system B are 

 made long enough to pass through wide conical holes cut in the 

 top and bottom plates of system A, and the nuts at the top end 

 ot the bolts are also conical in form, while conical nuts are also 



1 Thomsonand Tail's " Natural Philosophy," § 198 example 3. 



NO. II 83, VOL. 46] 



