294 Improvements on a Dew-point Hygrometer. 



washers, in bringing the bottle T\'ith the inserted thermometer into 

 the proper vertical position. This inconvenience has been com- 

 pletely remedied by connecting the neck of the bottle v^^ith the 

 syringe by means of a coupling screw, instead of an ordinary screw. 

 In this way the bottle and thermometer can be at once brought 

 into any required position, without the use of any washer at all on 

 that side; and as the screw projecting from the ivory collar on that 

 side is now made of brass, instead of being of ivory as before, it is 

 not subject to fracture when any little additional force is necessary 

 in order to unscrew it. In this way both additional facility of 

 manipulation and additional security from accident are attained. 

 This alteration also creates much greater facility of attachment, 

 according to the varying nature or position of the fixtures to 

 which the clamp which secures the instrument when in opera- 

 tion is made fast. The form of the key employed in screwing 

 and unscrewing the bottle and ivory collar has also been altered 

 in a way which does not risk the fracture of the collar as the 

 previous one did. It now grasps the collar externally, like that 

 used for an air-pump or gas-holder. The new forms of screw, 

 ivory valve-piece, and key, can easily be adapted to any instru- 

 ment which has been constructed in the original manner. 



It is also satisfactory to be able to state, that during this 

 summer I have had ample experience of the instrument being 

 in all its parts quite calculated to stand the ordinary concussions 

 of travelling, having carried it with me in its proper case in my 

 ordinary baggage, during a tour on the Continent, without injury 

 to any part of it. On this occasion I have also found that it 

 worked equally well as at home, in the various situations in 

 which I employed it in Germany, Switzerland and France*. 



It may be mentioned that the gold-beater's leaf valve is con- 

 structed by folding a piece of that material, 2 inches long by 

 i an inch wide, first longitudinally and then transversely. This 

 fourfold portion is then placed across the valve-piece and secured 

 in its place by two or three coils of silk thread, and the super- 

 fluous leaf and thread cut away by a sharp pen-knife. A drop 

 of sperm oil on the point of the knife is then passed care- 

 fully under the leaf and the knife instantly withdrawn. Gentle 

 pressure by the point of the finger causes the oil to pass over 

 the whole surface under the leaf. The proper state of the valve 

 is ascertained both by blowing and suction. 



* In order to meet the wishes of those who may desire to find their own 

 bottles for aether and ohve oil, Mr. Kemp of Edinburgh has fitted up all 

 the essential parts of the instrument in a smaller and less expensive case, 

 which he finds he can afford to sell at two-thirds of the cost of the more 

 complete arrangement; those, however, who may wish to have everything 

 necessary at their hand, can still obtain from him the complete collection 

 in their proper case. 



