2 SECTION PHYSICS. 



To mention only a few among the many foreign institutions which 

 have contributed to this undertaking, we are specially indebted to the 

 authorities of the Conservatoire des Arts et Metiers of Paris, the 

 Physical Museum of Leyden, the Tayler Foundation of Haarlem, the 

 Royal Museum of Berlin, the Physical Observatory of St. Petersburg, 

 the Tribune of Florence, and the University of Rome. 



Among those in our own country, we have to thank the Royal 

 Society, the Royal Institution, the Ordnance Survey, the Post Office, 

 the Royal Mint, the Kew Observatory, besides various other institu- 

 tions and colleges, which have freely contributed their quota. 



To enumerate even the chief of the individual instruments of his- 

 torical interest would be a task beyond the limits both of my powers 

 and of your patience. But I cannot refrain from naming as especially 

 worth notice among the astronomical treasures, a quadrant of Tycho 

 Brahe', telescopes of Galileo, a telescope of Newton, some lenses by 

 Huygens, one of Sir W. Herschel's grinding machines for specula, 

 and a telescope made by himself in intervals between his music 

 lessons during his early days at Bath, at a time when, to use her own 

 words, his sister Caroline " was continually obliged to feed him by 

 putting victuals by bits into his mouth." This also is probably the 

 "mirror from which he did not take his hands for sixteen hours 

 together," and with which he may have seen for the first time the 

 Georgium Sidus. To come to later days, we have the original 

 siderostat of Foucault, lent from the Observatory of Paris, a com- 

 pound speculum by the late Lord Rosse, the photoheliograph from 

 Kew, and from still more recent times a complete transit of Venus 

 equipment, from the Royal Observatory at Woolwich. 



Turning to other branches of physics, we have a " composed 

 microscope," now nearly three centuries old, constructed in 1 590 by one 

 Zacharias Janssen, a spectacle maker, possibly a connection, or at all 

 events a worthy predecessor, of M. Janssen, the celebrated astronomical 

 spectroscopist. We have an air-pump and two " Magdeburg hemi- 

 spheres," with the original rope traces by which horses were attached 

 in the presence of the Emperor Charles V., in order, if possible, to 

 tear them asunder, when exhausted by the air-pump. We have the 

 air-pump of Boyle, the compressor of Pappin, Regnault's apparatus 

 for determining the specific heat of gases, Dumas' lobe for the 



