Account of an Improved Hygrometer. 127 



so long as any electricity is brought down by the conductor. 

 As the insulation of the pith ball is easily insured, this form 

 is more delicate than electrometers with two pith balls, or 

 even those of gold-leaf. 



% Account of an Improved Hygrometer. 



It has occurred to several meteorologists, that Mr DanielFs 

 hygrometer might be simplified, by applying the ether direct- 

 ly to the ball of a simple thermometer. Mr Jones of London 

 employs a thermometer with a ball of black glass, and bent 

 twice at right angles, in order (so far as we can judge from a 

 very imperfect description of the instrument in Mr Brande's 

 Journal) to bring the deposition surface more easily on a 

 level with the eye of the observer. When one part of the 

 ball is moistened with ether, the vapour of the atmosphere is 

 condensed upen the other, and the temperature at which this 

 takes place is noted. A similar method has been used during 

 the last summer by a correspondent who has favoured us with 

 a description. A thermometer, with a ball of black glass, has 

 adapted to it, by gum arabic, a ring of silver, (as in Plate I. 

 Fig. 32.) the upper part of the ball being covered with mus- 

 lin. By this contrivance, the ether, when dropped on the 

 muslin, is prevented from reaching the lower part of the ball 

 on which the dew is deposited ; and, unless some method of 

 this kind be used, we do not see how it is possible to insure 

 accuracy of observation. It has been suggested to us by 

 several practical meteorologists, that, in this arrangement, 

 there is a possibility of error from the circumstance of the de- 

 position surface not being in immediate connection with the 

 stem, or that part which indicates the temperature of the in- 

 strument. Should this suggestion be found correct, it will 

 be necessary to employ a thermometer, bent as in Plate I. 

 Fig. 33. If the ether be dropped on the upper part of the 

 ball (a) the vapour is condensed upon the lower portion, 

 which is the part that gives the temperature of deposition, 

 and every chance of error is avoided. 



N. 



