II. AIK PUMPS, ETC. 131 



588. Sprengel's Mercury Pump. 



The Director of the Physical Laboratory of the University 

 of Gronwgen. 



This instrument differs from all others (1) in the numerous curvatures of 

 the tube through which the mercury falls. These augment the evacuating 

 power of the pump, while the air bubbles, which are carried away with the 

 mercury, and which, when near vacuum, are so minute that they remain 

 hanging on the walls of the tubes before coming down, assemble in the curva- 

 tures, until their size is so far augmented that they are earned away by the 

 falling mercury. (2) The instrument is provided with a peculiar stop-cock 

 with two perforations, whereby the flowing of the mercury is regulated and 

 the acquired vacuum preserved. To effect this, the stop-cock is furnished 

 with two iron rings, which float on the mercury, and, falling with it, close the 

 opening of the stop-cock. By means of the second perforation of the stop- 

 cock the instrument can be joined to an ordinary air pump, and the operation 

 abridged by a partial exhaustion of the air. To produce a more complete 

 vacuum than can be obtained by an ordinary air pump, the stop-cock is turned 

 half round, and, when the vessel surrounding the stop-cock is filled with 

 mercury, Sprengel's air pump begins to act. 



589. Aspirator, moved by clockwork and sulphuric acid ; 

 U tube for determining accurately the amount of moisture in the 

 atmosphere by the use of the balance. Dr. Andrews, F.R.S. 



The amount of moisture at different periods of the day, or the average 

 amount in 24 hours, may be determined with great precision by means of this 

 arrangement, which Dr. Andrews proposed many years ago for use in meteor- 

 ological observatories, instead of the present defective methods. 



590. Spirator. Designed to get a constant current and 

 measureable volume of air driven or drawn over a body. 



Frederick Guthrie, F.R.S. 



The principle resembles that of " Tantalus' cup." A constant current of 

 water enters a flask, and (1) drives out its own volume of air through a 

 mercury trap ; (2) when the flask is filled up to a certain point, a siphon acts, 

 and, in emptying the flask, draws air in from another tube. 



591. Small Wooden Model of Mr. Colladon's new Air 

 and Gas Compressors (patented), used for the great Gothard 

 Tunnel. Professor Daniel Colladon, Geneva. 



This system of compressors refrigerates air and gases simultaneously with 

 the compression, and all the moveable parts are kept cold, whatever may be 

 the rapidity and force of compression. This system has been applied to 

 several industrial purposes. It is the system of air compressors used exclu- 

 sively in the boring of the great Gothard tunnel (length 14,920 metres). 

 At the extremity of this tunnel 30 of these compressors give 40 cubic metres 

 of air per minute, under the pressure of seven atmospheres, for the aeration of 

 the tunnel, and the working of 60 boring machines and other apparatus, and 

 eight other compressors supply air of 14 atmospheres for compressed air 

 locomotives. See 2O6O. 



597. Air Pump, by Otto von Guericke, with stand. 



Professor Dr. Lcpsius, Berlin. 

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