H. AIR PUMPS, ETC. 135 



the barrel is placed in a diagonal position, and the pump provided with glass 

 plate and stop-cock, but if the plate with the cock be screwed off, and 

 the hose-screw attached to the wooden stand screwed on, and the barrel 

 detached from its support and placed perpendicularly, the pump can in that 

 case be used as a compression pump. Plate with cock are meanwhile 

 screwed again on the wooden stand. The cock below the barrel, by reason of 

 its parallel position, effects with this the connexion between barrel and plate, 

 and in its upward position, the communication between barrel and the external 

 air ; and, lastly, in its downward position, the communication between the 

 plateau and the external air. 



601. Mercury Air Pump, on Professor von Jolly's system, 



Professor von Jolly, Munich. 



This air-pump has been described by G. Jolly in Carl's Repertorium, 1865. 

 As regards the alterations which have since taken place, and which have been 

 introduced in the apparatus exhibited, a special description has been added 

 to the object. 



602. Apparatus for proving Mariotte's and Dalton's 

 Law. 



Professor Baron Dr. von Feilitzsch, University of Greifs- 

 wald. 



Whilst, commonly, two different apparatus aie employed for demonstrating, 

 for a larger or a lesser pressure than one atmosphere, the laws in question, 

 this inconvenience has been remedied by the present apparatus. A glass 

 tube open at the upper end, and a gauged glass tube, which can be closed at 

 the upper end by a stop-cock, communicate by means of a long gutta-percha 

 tube, can be displaced on a vertical scale, and are partly filled with mercury. 

 The latter tube contains the gas to be tested, or the combination of gases and 

 vapours, and by raising or lowering of the first tube, the level of the mercury 

 will be changed as required, and the volume of gas resulting therefrom indi- 

 cated. 



The apparatus can be easily employed, if suitably altered, for all kinds 

 of experiments, at which different pressure, or a reduction to the atmospheric 

 pressure is required ; for instance, in atmospherical thermometers, &c. 



603. Air Pump, by J. van Musschenbroek, and two Magde- 

 burg hemispheres. 



The Royal Museum at Cassel, Dr. Pinder, Director. 



1. Air-pump, ivith obliquely placed cylinder, on Senguerd's system. 



This air-pump is, perhaps, the oldest of the kind existing, with a doubly 

 perforated stop-cock, as will be seen by the following explanations. It Avas 

 constructed in the! year 1786, by Jan van Musschenbroek, in Leyden ; nor is 

 it wanting in the Musschenbroek's emblems, namely, the " Ostor lamp," and 

 the crossed keys ; the armorial bearings (i.e., coat of arms) of the city of 

 Leyden. The invention of the doubly perforated stop-cock, notoriously origi- 

 nated Avith Senguerd, who, from the year 1675-1724, was professor at Leyden. 

 The air-pump, which is preserved in the Physical Science Cabinet of that town, 

 and which, according to the inscription, was constructed by Samuel Mus- 

 schenbroek, in the year 1675, and Avhich has a doubly perforated stop-cock, 

 Avhich is considered there as the first of the kind, could not at first have been 

 provided Avith it, as it was invented at a later date. It has been, with its com- 

 ponent parts, applied to it only at a later period. Senguerd has described 

 that kind of cock for the first time in the second edition of his " Ph'losophia 



