160 SEC. 0. MOLECULAR PHYSICS. 



earlier forms of having two barrels, in which case, as the air becomes 

 exhausted, the resistance which it offers to the ascent of one piston is nearly 

 balanced by the force with which it compels the other to descend. This air- 

 pump was worked by moving the feet alternately up and down in stirrups. 



626. Diagram of Hauksbee's Air Pump. 1703-9. 



A. Galletly, Edinburgh. 



This instrument, like Papin's, had two barrels, but the stirrup arrangement 

 and pulley are replaced by racks on the piston rods, and a pinion moved by a 

 handle, as in the modern double-barrelled air-pump. These diagrams 622- 

 626 were made to illustrate a paper on the early history of the air-pump, pub- 

 lished in the New Philosophical Journal, April 1849, by the late Dr. George 

 Wilson of Edinburgh. 



687. Diagram of Torricellian Vacuum. 1644. 



A. Galletly, Edinburgh. 



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

 burg hemispheres. 



The Royal Museum, Cassel, Dr. Pindcr, Director. 



1. Air-pump, with obliquely placed cylinder, on Seng uercl' 's system. 



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

 way" stop-cock. It was constructed in the year 1786, by Jan van Mus- 

 schenbroek, in Leyclen, and bears the Musschenbroek arms, namely, the 

 " Oosterche lamp," and the crossed keys ; the armorial bearings of the city of 

 Leyden. The invention of the four way stop-cock notoriously originated 

 with Sengucrd, who, from the year 1675-1724, was a professor at Leyden. 

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

 according to the inscription, was constructed by Samuel Musschenbroek, in 

 the year 1675, and which has a four way stop-cock, is there considered 

 to be the first of the kind, but could not at first have been provided 

 with this adaptation since it was invented at a later date. This appliance 

 must have been adapted to it only at a later period. Senyuerd first described 

 this kind of cock in the second edition of his " Pbilosophia Naturalis," 

 which was published at Leyden in the year 1685. In his work, " Rationis 

 atque Experimentise Connubium," which was published at Rotterdam in the 

 year 1715, he states that he made the invention in 1675, and that in 1679 

 he had the air-pump executed by a skilful artizan. That this artizan was 

 Samuel Musschenbroek is proved by a notice in the handwriting of Petrus van 

 Musschenbroek, which he wrote in a copy of his work entitled, " Beginselen 

 der Naturkunde." HoAvever, Senguerd, in the first edition of his work, 

 ' Philosophia Naturalis," which appeared in 1680, and of which a copy is in 

 the possession of the Library of the University at Utrecht, makes no men- 

 tion at this time of the cock, but gives an illustration of an air-pump of the 

 original construction of Otto von Guericke. That the air-pump was con- 

 structed is plain, from a record of Offenbach's, describing the " Laboratoriuin 

 Physicum " of the University of Leyden, dated the 19th January 1711 : 



" In the centre stood an elevated table. Upon this table there stood an 

 " * Antlia pneumatica ' of considerable size, of Samuel Musschenbroek' s old 

 " invention, inclined with a ' cista ' to put water in." Although the words 

 " from the invention of Sam. Musschenbroek " may also have reference to 

 the air-pump, which is still preserved in the Physical Science Cabinet at 

 Leyden, yet the description does not tally with it, inasmuch as its cylinder 

 is perpendicular, and stands next to an elevated table which carries the 

 plate, and is consequently united with it in one apparatus. It is possible 

 that Uffenbach, who was not an adept in that science, was only induced to make 



