DR. C. IV. SIEMENS' ADDRESS. 215 



chemical affinity between the two liquids. Several thousand instru- 

 ments of this description are employed by the Russian Government 

 in controlling the production of spirits in. that empire, whereby a 

 large staff of officials is saved, and a perfectly just and technically 

 unobjectionable method is established for levying the excise dues. 



Another instrument, not belonging to any of the classes enume- 

 rated, is one for measuring the depth of the sea without asounding 

 line, which has recently been designed by me, and described in a 

 paper communicated to the Royal Society. Advantage is taken in the 

 construction of this instrument, of certain variations in the total 

 attraction of the earth, which must be attributable to a depth of 

 water intervening between the instrument and the solid constituents 

 of the earth. It can be proved mathematically that the total gravita- 

 tion of the earth diminishes proportionately with the depth of water, 

 and that if an instrument could be devised to indicate such minute 

 changes in the total attraction upon a scale, the equal divisions on 

 that scale would represent equal units of depth. 



Gravitation is represented in this instrument by a column of mercury 

 resting upon a corrugated diaphragm of thin steel plate, which in its 

 turn is supported by the elastic force of carefully tempered springs 

 representing a force independent of gravitation. Any change in the 

 force of gravitation must affect the position of this diaphragm and the 

 upper level of the mercury, which causes an air-bubble to travel in a 

 convolute horizontal tube of glass placed upon a graduated scale, the 

 divisions of which are made to signify fathoms of depth. Special 

 arrangements were necessary in order to make this instrument 

 parathermal, or independent of change of temperature, as also 

 independent of atmospheric density, which need not be here de- 

 scribed. Suffice it to say that the instrument, which has been placed 

 on board the S. S. "Faraday" during several of her trips across the 

 Atlantic, has given evidence of a remarkable accordance in its indica- 

 tions with measurements taken by means of Sir William Thomson's 

 excellent pianoforte wire-sounding machine ; and we confidently 

 expect that it will prove a useful instrument for warning mariners of 

 the approach of danger, and for determining their position on seas, 

 the soundings of which are known. 



Another variety of this instrument is the horizontal attraction 



