DISCOURSE OF W. B. TAYLOR. 271 



and afterward independently, as well as mediately in directing his 

 own pupils and assistants. In 1833, he devised an improvement 

 on Wollaston's mechanical scale of the chemical equivalents, for the 

 benefit of his pupil- in chemistry: — a contrivance which was much 

 used and highly appreciated at the time. 



The suggestion had been thrown out by more than one astron- 

 omer, that carefully timed observations on characteristic meteors 

 or "shooting-star-" might be made available for determining 

 differences of longitude between the stations of observation.* For 

 many years however the proposition had been generally regarded 

 as offering rather a speculative than a practical method of solving 

 a problem of so great nicety. Henry in concert with his brother- 

 in-law, Professor Alexander, and with his friend Professor Bache, 

 determined to ascertain by actual trial the availability and value of 

 the svstem. On the 25th of November, 1835, Professor Bache 

 observing at hi- residence in Philadelphia (assisted by Professor J. 

 I'. Espy,) — simultaneously with Professor Henry and Professor 

 Alexander, at the Philosophical Hall at Princeton, they obtained 

 -even co-incidences: — the instant of disappearance of the meteor 

 being in each case selected as the most accurately attainable epoch. 

 These seven observations (whose greatest discrepancies amounted to 

 but a trifle over :; seconds] gave a mean result of 2 minute- 0.61 

 second (time longitude), differing only one second and two-tenths 

 from the mean estimate of relative longitude arrived at by other 

 methods. ; 



In 1840, Henry gave an account of "electricity obtained from a 

 small ball partly filled with water, and heated by a lamp."J 



"The merit Of first suggesting tie- usr of shooting-stars and fire-balls a- Mu r ii:iU 

 for th.' determination of longitudes i- claimed by Dr. Olbers ana th.- German 

 astronomers for Benzexberg, who published a work on the subject in 1802. Mr. 

 Bailey however has pointed o,ut a paper published by Dr. Maskelyxe twenty 

 year-- previously, in which that illustrious astronomer calls attention to the sub- 

 ject, and distinctly point- out this application of tin- phenomena." This was 

 dated Greenwich, X.. v. -nil. .a- 6th, IT-;. /.. /:. D. Phil. Mag. 1841, vol. xix. p. 551 



\Proceed. Am. Phil. Soc. Dec. 20, 1S39, vol. i pp. 102, 163. "This appears to have 

 i i the first actual determination of a difference of longitude by meteoric obser- 

 vations." i /.. E. IK Phil Mag. isll. vol. xix. p. 553.) Several years later in 1838 

 lar meteoric observations were made between Altonu and Breslau; and also 



betW een K illle alal Naples. 



; Proa ed. Am. Phil. Soc Dec. 18, 1840, vol. i. p. 323. 



