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XXX L Remarks on Hygrometry, and the Hygrometer of 

 J. Birzelius. In a Letter from Mr. J. Gough, to 

 Mr. Til loch. 



Middleshaw, Feb. 25, 1809. 



X erhaps few additions could be made at present to the ap- 

 paratus of a meteorologist, which would prove more accept- 

 able than a cheap and correct hygrometer. Various attempts 

 have been made to improve the instrument, which have 

 commonly ended in adding to its sensibility : but such con- 

 trivances seem intended to amuse the superficial observer, 

 rather than to assist the lover of meteorology. It is the 

 business of those who cultivate this science, to determine 

 the comparative humidity of the atmosphere, not only as it 

 is found in different parts of the world, but also as it varies 

 with situation in the same country. This project would be 

 carried into effect with the greatest ease and certainty, by 

 diminishing the sensible powers of the hygrometer rather 

 than by improving them. The preceding proposal is far 

 from being new; for the same notion respecting hygrometry 

 occurred to Dr. Franklin, so long ago as the year 1764. 

 The idea was suggested to the Doctor by an incident, which 

 proves the atmosphere to be drier in Pennsylvania than it is 

 in England and France. The Doctor's thoughts on the sub- 

 ject appeared in the first volume of the American Philo- 

 sophical Transactions, under the form of a letter addressed 

 to Mr. Nairne, of- London, in 1/80 : and it is superfluous 

 to add that his sentiments are delivered with the elegance 

 and perspicuity which distinguish the productions of this 

 great man. 



I have entertained an opinion for some time past, that a 

 common artist might construct an instrument which would 

 answer the purposes already specified ; and a few experi- 

 ments were made under mv direction three or four years 

 ago, which were far from discouraging the hope. The plan 

 of the hygrometer here alluded to is very simple, and will 

 be easily understood from the following description, assisted 

 by the annexed figure. 



Vol. 33. No. 131. March 1809. M In 



