Mr. T. Tate on a new Evaporameter and Absorb ometer. 127 



tube E F. The pillar F G admits of being raised or depressed, 

 so as to give any desired inclination to the tube E F. A mark 

 is made on the surface of the glass bell at D, a little below the 

 ordinary level of the water, with which the graduations on the 

 displacement-tube are at each observation compared; also a 

 special mark is made on one of the graduations of the tube E F 

 at a, towards its outer extremity, with which the water in the 

 tube at each observation is made to coincide by raising or de- 

 pressing the displacement-gauge. Now as the water in the tube 

 always stands at a point depending on the height of the water in 

 the glass bell, any slight depression of the water in the bell, pro- 

 duced by evaporation or by any other means, will cause the water 

 in the tube to move through a comparatively large space; thus 

 if the tube has a rise of — in 5, then a fall of jgth of an inch in 

 the bell will cause the water in the tube to fall through the space 

 of an inch ; that is, the scale of reading in this case will be in- 

 creased fifty times ; moreover, if the displacement- gauge be de- 

 pressed until the water in the tube is brought again to the 

 position a, the reading of this gauge will give the number of 

 cubic inches of water evaporated. 



To adjust the inclination of the tube E F so as to give any 

 proposed scale of reading. — Let it be required, for example, to 

 give the tube such an inclination that one cubic inch depression 

 of the gauge shall cause the water in the tube to move through 

 the space, say, of half an inch. The zero-mark on the displace- 

 ment-gauge being made to coincide with the mark D on the 

 glass bell, water is then added until it reaches a certain mark on 

 the tube; the gauge is then depressed until the mark of one 

 cubic inch coincides with the mark on the bell, and the space 

 through which the water in the tube has moved will show 

 whether the inclination of the tube is too much or too little, and 

 then the moveable pillar G F is lowered or raised accordingly ; 

 and this is repeated until the proper inclination is found. In 

 order to obtain the true position of the water in the tube, it is 

 only necessary alternately to raise and depress the displacement- 

 gauge so as to cause the water to oscillate in the tube until it is 

 found to settle itself exactly at the same mark when the displace- 

 ment-gauge is brought to its desired position. This remark also 

 applies to all the ordinary observations made with the instru- 

 ment. This adjustment of inclination being once made, does 

 not require to be repeated, unless the place of the instrument has 

 to be changed, or unless some other scale of reading has to be 

 adopted. 



The instrument is ordinarily used in the following manner : — 

 At the commencement of the observations the displacement- gauge 

 is at zero, whilst the water in the tube stands at the mark a ; 



