.S7A' WJl.u.i.M SIEMENS, FJtS. 379 



height of 185 feet, the aneroid indicating a difference of 208 feet. 

 This difference of readings may appear at first sight excessive, 

 but may be accounted for by disturbance of the instrument in 

 inking it by hand up the steep steps of the tower, where little 

 time \v;is allowed to insure the complete readjustment of the 

 roliunn. In this case also the reading of the instrument gives a 

 result inferior to the indications of theory as compared with it 

 indications on board ship, which latter indications I consider arc 

 t he more reliable, because the instrument, when once suspended, is 

 not disturbed, and its indications are rendered more delicate 

 through the oscillations of the vessel. 



MODIFICATIONS IN THE INSTRUMENT. The instrument, as 

 constructed at present, leaves room for such improvements as 

 have partly been, and are likely still to be, suggested by experi- 

 ence. It would be possible to eliminate entirely the effect of 

 variation of temperature by more carefully proportioning the 

 diameter of the mercury column to that of the cup. The in- 

 fluence of variation of density of the atmosphere might also be 

 entirely eliminated if the spaces in the cups above and below the 

 mercury column were closed against the atmosphere, and were 

 brought into communication with each other. The mode of 

 reading the instrument may also be simplified in various manners, 

 or the instrument may be made self-recording by the addition of 

 a chronograph. My present object has been to demonstrate the 

 possibility of constructing a bathometer capable of giving indica- 

 tions of moderate variations in the depth of sea below a vessel, 

 and to describe rather the instrument actually used than such 

 modifications as may prove more advantageous hereafter. 



PRACTICAL USES OF BATHOMETER. The useful purposes for 

 which a bathometer, so arranged as to be observable without 

 difficulty by the commander of a ship, may be employed, are, I 

 think, apparent. It often happens at sea that through clouded 

 skies and fogs it is impossible for astronomical observations to be 

 taken, and it is well known that the compass and dead-reckoning 

 are very uncertain guides to the position of a ship ; and as the 

 sounding-line can only be of assistance after the ship has arrived 

 at such depths as are positively dangerous, many calamities are on 

 record where, under such circumstances, not only sailing-vessels, 

 but well-equipped steamers have run ashore. The indications of 



