382 THE SCIENTIFIC PAPERS OF 



connecting-tube ; the upper halves of the cast-iron transverse 

 tubes and the glass connecting-tube are filled with alcohol tinted 

 with cochineal, comprising, however, a small bubble of air, which 

 can be made to occupy a central position in the glass tube by 

 raising or lowering the set-screws. 



If a weighty object is approached to either extremity of the 

 connecting-tube an attractive influence will be exercised upon the 

 mercury, tending to a rise of level in the reservoir near at hand, at 

 the expense of the more distant reservoir ; and this disturbance of 

 level between the two reservoirs must exercise a corresponding 

 effect upon the index of air in the horizontal glass tube, moving it 

 away from the source of attraction. The amount of this move- 

 ment must be proportionate to the attractive force thus exercised, 

 and is considerable, because the transverse cross section of each 

 reservoir-tube is 60x300=18,000 square millims., whereas the 

 section of the glass tube is only about 3 millims. ; the motion 

 produced by the effect of gravity is thus increased 3,000 fold, and 

 could easily be increased, say 30,000-fold, by simply increasing the 

 horizontal area of the transverse or reservoir-tubes. Variations of 

 temperature have no effect upon this instrument, because the 

 liquids contained on either side of the index of air are precisely 

 the same in amount ; and the total expansion of the liquids is 

 compensated for by an open stand-tube rising up from the centre 

 of the connecting-tube, through which the apparatus can be easily 

 filled. By means-of this instrument the effect of 1 cwt. approached 

 to one end or the other of the mercury connecting-tube causes a 

 sensible motion of the air index. 



It is suggested that an instrument of this description may be 

 employed usefully for measuring and recording the attractive in- 

 fluences of the sun and moon which give rise to the tides. The 

 instrument, which is of simple construction and not liable to 

 derangement from any cause, would have to be placed upon a 

 solid foundation with its connecting-tube pointing east and west, 

 records being taken either by noting the position of the index 

 upon the graduated scale below, or by means of a self-recording 

 arrangement through photography. 



This mode of multiplying the effect produced by gravitation is 

 applicable also to the bathometer ; and one of these instruments 

 was shown which was fitted with a spiral glass tube laid 



