March 30, 1876] 



NA TURE 



431 



The scientific culture which pervades the educated 

 classes of Germany is usually ascribed to the efficiency 

 of the Universities ; I believe it would be more correct 

 to put it down to the sound education in scientific matters 

 which the boys receive in the public schools, for it is only 

 the smaller number who proceed to the Universities : the 

 majority go after commercial and industrial pursuits. 



R. Gerstl 



University College School, London 



ON DETERMINING THE DEPTH OF THE SEA 

 WITHOUT THE USE OF THE SOUNDING 

 IINE ^ 



'T^HIS is the title of a paper which has been presented 

 -*■ to the Royal Society, and Mr. Siemens gave at the 

 meeting of the 24th ult, a description of the instrument 

 which he has designed with this object. He commenced 

 by giving a mathematical statement of the effect of local 

 attraction, to a certain depth, on a body placed at the 

 surface of the earth, assuming it to be of uniform density, 

 spherical in form, and unaffected by centrifugal action. 

 For small values of depth (//), this attraction is 2iTh, 

 the original formula from which this is adduced is : — 



-H-IV^). 



and by substitution oi 2 R for h in this, Newton's state- 

 ment of the total attraction ^Rtt\s obtained. 

 3 



Now, if in place of the solid substance which forms the 

 exterior crust of the earth, whose density may be taken to 

 be the mean density of superficial rock, water, a material 

 of less density is substituted, it is shown that the total 

 attraction must be diminished, and the measure of this 

 diminution is a measure of the depth of light substance 

 which has been substituted for heavy. If we were in 

 possession of the exact mean density of the earth, of that 

 of the surface-rock, and of sea- water, a scale could be 

 calculated beforehand, to show what depth would agree 

 with a certain diminution of the measured effect of gravi- 

 tation. Such an approximate calculation was made in 

 designing the instrument, but Mr. Siemens has preferred 

 to compare the readings of the instrument with actual 

 soundings, in order to obtain a scale. 



The instrument which is called a bathometer is repre- 

 sented in the accompanying illustration, and consists of 

 the following parts : a weight being a column of mercury 

 affected by variation of gravitation, a counterbalance being 

 springs unaffected by variation ofgravitatioi;, tnd an arrange- 

 ment by which the variations in gravitation can be read as 

 depth in unit?. The column of mercury is maintained in 

 a vertical steel tube having cup-like extensions, the lower 

 portion being closed by a corrugated diaphragm of thin 

 steel plate, and the upper portion containing an aperture 

 for filling the instrument, having a screw stopper. The 

 internal diameter of the tube is reduced at the upper 

 portion, in order that the vertical oscillations of the 

 mercury produced by the motion of a vessel in a sea-way, 

 may be reduced to a minimum, and the instrument is 

 suspended in a universal joint above its centre of gravity, 

 so that it may always hang in a vertical position at sea, 

 and is enclosed in an air-tight casing so that it may not 

 be under the influence of atmospheric changes. The 

 weight of the column of mercury is balanced at the centre 

 of the diaphragm by the elasticity of the steel springs, 

 and the modus operajidi of the instrument is evident ; as 

 the mercury diminishes in potential through the effects of 

 diminished attraction, the action on the springs diminishes, 

 and these shorten upon themselves. 



There are some peculiarities in the mechanical arrange- 

 ment of the instrument which repay examination. Both 

 ends being open to the air, its indications are not 



By C. William Siemens, D.C.L., F.R.S. 



affected by variations of atmospheric pressure. With 

 regard to temperature, the instrument is parathermaL 



Its peculiar form has been the result of scientific inquiry. 

 It was first discovered by experiment that well-tempered 



steel springs diminished in potential with rise of tempe- 

 rature in a constant ratio, it was therefore necessary that 



