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XI. Experiments on Aneroid Barometers at Kew Observatory, and their Discussion. 



By C. CHREE, Sc.D., LL.D., F.R.S., Superintendent. 

 Communicated by the Author at the Request of the Kew Observatory Committee. 



Received May 5, Bead June 9, 1898. 



TABLE OP CONTENTS. 



SECTIONS. PAGE 



1. Preliminary 441 



2, 3, General character of phenomena ; apparatus 442 



4-6. Differences of descending and ascending readings, from Kew verifications .... 444 



7, 8. Differences of descending and ascending readings, from special experiments . . . 448 

 9. Formulae for variation of the differences of descending and ascending readings 



throughout the range 451 



10. Position of maximum difference, descending less ascending reading 452 



11-15. Relations between phenomena over different ranges 453 



16-19. Pall of reading at the lowest pressure 457 



20, 21. Recovery after pressure cycle 461 



22-25. Effects of temperature 463 



26-29. Secular change in aneroids 468 



30-33. Influence of rate of change of pressure 473 



34-41. Effects of stoppage 480 



42-46. Theoretical deductions 487 



47-54. Discussion of previous work 492 



55, Conclusion, acknowledgement of assistance 499 



Preliminary. 



1. THE ordinary aneroid barometer is an instrument whose chief recommendations 

 are its portability and the ease with which it can be used by travellers. It is essen- 

 tially a field instrument, and it would be largely waste of time to treat it as if 

 intended for the laboratory. 



The first object of the present investigation is to acquire knowledge likely to 

 increase the usefulness of the aneroid under the conditions in which it is actually 

 employed. 



Aneroids have for many years been tested at Kew Observatory, and records exist 

 of the performance of many hundreds of various sizes. The test has hitherto been 

 applied as follows : The aneroid has been put in the receiver of an air pump, and, 



VOL. CXCI. A. 3 L 11.10.98 



