136 SEC. 5. MOLECULAR PHYSICS. 



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

 " Rationis atque Experimenta 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 Avas 

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

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

 der Natuukunde." However, 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 yet of the cock. He has therein an illustration of an air-pump of the 

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

 constructed is plain, by a record of Uffenbach's, who, in describing the 

 " Laboratorium Phyricum " of the University of Leyden, stated on the 19th 

 January 1711 : 



" In the centre stood also 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 

 " of the invention of Sam. Musschenbroek " may also be applied or 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 making the above-mentioned expression by the sign of the firm of S. v. 

 Musschenbroek. But how it happened that he did not see the other air-pump, 

 since he mentions yet another still existing air-pump of Boyle's construction, 

 is rather obscure, as De Voider, Senyuerd's predecessor in the professorship of 

 physics at Leyden, who himself has laid the first foundation for the establish- 

 ment of the Physical Science Cabinet at Leyden, must have worked in the 

 same laboratory. "As we were assured," continues Uffenbach in his narratives, 

 " there are given here (in the laboratory) ' Lectiones publicae ' four times a 

 " week by M. Senguerd, De Voider, however, it was stated, has had more 

 " auditors, as he was also more artful (' curieuser ') in his experiment." 



Senguerd delivered those lectures not until after De Voider' s retirement, 

 in 1705. De Voider, however, died in 1709, and it is possible that the air- 

 pump was at that time in course of reconstruction. Senguerd' s air-pump, 

 therefore, as it is not to be found in the Physical Science Cabinet at Leyden, 

 must, in all probability, have been private property ; and it is possible that, 

 like many old instruments, it is still somewhere in private possession in Hol- 

 land. So long, however, as it is not discovered, the Museum at Cassel may 

 lay claim to the distinction of having in its possession the air-pump with the 

 oldest doubly-perforated stop-cock. For although Senguerd had his air- 

 pump made in 1679, the description of the same did not appear until 1685, 

 which indeed excited much attention at the time. Christian Wolff, in 1718, 

 had one constructed exactly according to the same pattern, by Leupold at 

 Leipsic, which may still be seen in the Physical Science Cabinet of the Uni- 

 versity at Marburg. Very singular indeed it is that Musschenbroek, in his 

 manifold writings, never as much as mentions Sengucrd's air-pump. That, 

 of course, this omission cannot be constructed into an argument as against 

 the priority of Senguerd is plain by the subsequent remarks in the above- 

 mentioned autograph notice, in which it is stated that "in the year 1679 

 " Mr. Senguerd considered with the same Samuel Musschenbroeh air-pumps 

 " of another kind, which afterwards were improved by my father, Jan van 

 " Musschenbroek, as well as by my brother " ("in den jaare 1679 heeft de 

 " Heer Seuguerd met dienzelven Samuel Musschenbroek hucht pompen van 

 " een anderen aart bedagt, welke geduurig naderhand door rnynen vader 



