the South African Institution. 105 



his offer of a premium of Rds. 50, for the best specimen of 

 Cape grown Leaf Tobacco: the two latter to be awarded at the 

 Annual General Meeting in June. — There was read a paper by 

 Mr. Reid, Member of the Institution,* on the Salts of Mercury, 

 and some of their combinations, used in Pharmacy, (printed 

 in this Number of the Journal). Dr. Adamson* Secretary, ex- 

 hibited and described a Thermometer, intended to register the 

 variations of temperature at all times. This consisted of a 

 Thermometer of a peculiar construction, suspended so as to 

 vibrate like a balance upon an axis, and mark the variations of 

 temperature by tracing a line upon a surface. The object was 

 eflected by the following arrangements : — a sufficient degree of 

 varying preponderance must be given to one extremity of the 

 tube, to overcome the friction with which the tracing point has 

 to contend ; which cannot be attained by filling the ther- 

 mometer with mercury or alcohol alone, because the quantity 

 by which mercury expands for one degree, is too small to affect 

 sufficiently the friction of the instrument, even when suspended 

 in the most delicate manner, and the weight 9!' a column of 

 alcohol is too little to produce the requisite power by its greater 

 expansion. We must, therefore, employ the expansion of the 

 lighter fluid, combined with the" weight of the heavier one. 

 The instrument exhibited, consisted of a tube having a diameter 

 of about one sixteenth of ary inch, with a bulb at each end. 

 The larger bulb was filled with transparent alcohol, wKich by 

 its expansion moved a column of mercury, filling {he whole of 

 the tube connecting the bulbs. The smaller bulb serves simply 

 as a reservoir into which the mercury may be driven. The 

 shifting of the centre of gravity of this column of mercury, 

 affords the preponderance which we want, and the power of the 

 instrument, in this respect, will depend on the length and 

 weight of the 'column, and on the size of the bulb tilled with 

 alcohol. The materials must be so disposed that neither the 

 alcohol at one end nor the air at the other, have any oppor- 

 tunity of rising* through the mercury, in the different inclinations 

 of the instrument. It is, on this account, requisite to have a 

 piece of the tube adjoining to the bulbs, at each end, turned 

 upwards, and so to balance the instrument, that the tube when 

 quite filled with the mercury shall be horizontal. It would be 

 advantageous for the above-mentioned purposes, that the tube 

 should be of smaller bore, and that the mercury should partly 

 fill the lower parts of both bulbs; but in this case the gradu- 

 ation of the instrument could be effected only by comparison 

 with another. It is evident that the same method of producing 

 preponderance may be attained very readily in the sympie- 

 zometcr, so as to indicate the variations of barometric pressure. 



11 



