VOL. LXX.] PHILOSOPHICAL TRANSACTIONS. gSQ 



Dr. Priestley took a piece of the same wire, of exactly the same length, and 

 heated it red-hot in the common culinary fire. This wire, being afterwards 

 measured, was found to continue of its original length of 10 inches, not being 

 in the least shortened. Mr. N. generally found, that if the iron wire was 

 first annealed in the culinary fire, the same strength of charge melted it. 



Mr. N. also tried a piece of copper wire, gilt with silver, and of the same 

 dimensions as the iron wire, and found that the same charge, discharged through 

 it, shortens it -^ of an inch, viz. ■*- of what the iron wire was shortened. The 

 same strength of electrical charge, as near as could be measured by an electro- 

 meter, which passing through the iron wire, made it visibly red-hot in a bright 

 day, the sun shining at the same time, did not heat a piece of copper wire of 

 the same dimensions so as to appear of a red heat, though the room was made 

 dark. If the battery was but a little more charged, the iron wire then would be 

 melted; but it had no such effect on the copper wire. This seems to point out 

 that iron wire resists the passage of the electric fluid much more than copper; 

 and also that the culinary fire and electrical fire have different effects on iron and 

 copper: for malleable iron, it is said, is one of the most difficult metals to melt 

 by the culinary fire, and requires a much greater heat to melt than copper; 

 whereas, on the contrary, the iron is melted with a much less charge of 

 electric fire. 



XXI. Astronomical Ohservalions on the Periodical Star in Collo Ceti* By 

 Mr. fVilliam Herschel,-\- of Bath. p. 338. 



This remarkable star, we are told,;}: " was first observed by David Fabricius, 

 the 13th of August, IsgS, who called it the Stella Mira, or wonderful star; 

 which has been since found to appear and disappear, periodically, 7 times in 6 

 years, continuing in the greatest lustre for 15 days together, and is never quite 

 extinguished." 



My own observations, says Mr. H., on this wonderful star, are but few, yet 

 sufficiently verify the surprizing appearances that have been ascribed to it. They 

 are as follow. 



October 20, 1777, I looked out for it, but it was not visible. If its period is 

 312 days, it may be expected to be seen about Christmas. Dec. 18, 1777, I 

 saw the periodical star in collo Ceti. It was in magnitude about equal to ^, but 

 not so large as (J.§ Jan. 26, 1778, the periodical star was larger than ^, but 

 less than v. 



* Bayer's character for this star is «. 



+ See some authentic memoirs of this extraordinary character, in tlie European Magazine for 

 January 17S5. 



+ See Ferguson's Astronomy, ^ 366. 



§ { is marked by Bayer as a star of the fourtli magnitude, and ^of the third. 

 VOL XIV. 4 T 



