130 Prof. Poggendorff on a new form of ■ 



It is not until more than fifty years later that we find the 

 proposal made to revive the use of mercury for the purpose of 

 exhausting, by the construction of a special instrument. This 

 proposal proceeded from the celebrated theosophist Emmanuel 

 Swedenborg, who has described it in his Miscellanea observata 

 circa res naturales et prasertim circa miner alia, ignem et montium 

 strata, published at Leipsic in 1722. 



Swedenborg's pump consisted essentially of a little table with 

 three long legs, which carried the glass bell-jar that was to be 

 exhausted, and was connected below with an iron vessel, from 

 which descended perpendicularly an iron tube which was joined 

 by a flexible tube of leather with a second iron tube. By placing 

 this moveable tube upright or laying it down, the mercury which 

 filled both tubes was made to rise and fall, and thus the iron 

 vessel, which was provided with the needful valves, was alter- 

 nately filled with the liquid metal and emptied. 



This is the same principle as that employed by Joseph Baader 

 in his second mercurial pump ; he, however, improved the con- 

 struction by substituting a metal elbow-joint for Swedenborg' s 

 leather tube, but does not appear to have had any knowledge of 

 the idea of the latter*. In his first pump, which he had de- 

 scribed in 1784 in Hubner's Physikalisches Taschenbuch, the 

 descending and ascending tubes were connected together immo- 

 veably, and the lowering of the mercury in the exhausting- ves- 

 sel was caused by letting the proper quantity of the metal run 

 out through a cock placed at the lower part of the bend of the 

 tubes. By pouring into the upright tube, after shutting the 

 cock, the mercury that had run out, and opening the exhaust- 

 ing vessel so that the air which had been drawn in might escape, 

 the original state of things was reproduced. 



These pumps, however, which, so far as appears, were never con- 

 structed by their originators, have not met with the acceptance 

 of physicists ; and the same remark applies to all the pumps 

 which have been successively either proposed or actually con- 

 structed by Hintenburg, Michel, Cazalet, Kemp, Edelcrantz, Pat* 

 ten, Oechsle, Bomershausen, Uthe, Mile, Kravogl, and others > 

 in most of which the mercury was moved by means of a piston* 



It is only recently that the mercurial air-pump has attained a 

 better reputation, since the skilful glass-worker, Geissler of 

 Bonn, has employed it in the preparation of the exhausted tubes 

 with which his name is connected, and has by means of it ob- 

 tained a more perfect vacuum than could be produced by the 

 best piston-pump. 



* The merit of having been the first to call Swedenborg to memory 

 belongs to Gren, who gave the passage in question, together with the figure, 

 in his Journal der Physik for 1791 (vol. iv. p. 407). 



