14 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.C. 



21. Magnifying the Barometer Eange. The limit 

 within which the barometric column oscillates, does not 

 exceed four inches for extreme raDge, while the ordinary 

 range is confined to about two inches ; and it has often been 

 felt that the utility of the instrument would be much enhanced 

 if by any means the scale indications could be increased in 

 length. This object has been sought to be obtained by bend- 

 ing the upper part of the tube from the vertical, so that the 

 inches on the scale could be increased in length. Such an 

 instrument was invented by Sir S. Moreland, in 1772, and 

 named by him " the Diagonal Barometer." Another variation 

 of Barometer, invented by M. Cassini, and improved by M. 

 J. Benoulli, about the same date, was constructed with the 

 upper part of the tube expanded into a large Bulb, and the 

 lower part of the tube giving the scale is very much contracted 

 in the bore, and bent at a right angle. From this the instru- 

 ment was termed the Horizontal Rectangular Barometer. 

 The upper part of the Barometer tube has also been forme d 

 into a Spiral, with the scale placed along it, which is thus 

 greatly enlarged. 



Another form of Extended Range Barometer was in- 

 vented and made by M. Amontons in 1695, and named by 

 him the Pendent Barometer. It is a Mercurial Barometer, 

 the upper half of the tube (the indicating portion) being of 

 smaller internal diameter than the lower half. By this 

 arrangement, an extended range of scale is obtained. The 

 lower end of this tube is open, and the mercury supported in it at 

 varying distances by the upward pressure of the atmosphere, 

 very similar in action to that of Howson's Barometer. 



Like the previously described instruments, this Barometer 

 can only be regarded as a scientific curiosity, and is very 

 subject to become out of adjustment in transit. This is 

 unfortunate, as these Barometers are curiously sensitive, or 

 perhaps we should more properly say, the movements of the 

 mercury are rendered more visible. 



These methods of enlargement Barometer indications are 

 not so convenient as Dr. Hook's elegant arrangement em- 

 ployed in the ordinary Dial or Wheel Barometer. Therefore 

 they are now very little used, and are of very little practical 

 utility. 



FIG. 18. 



