•2\'l FHILOSOPHICAL TRANSACTIONS. [anNO 1751. 



The other place hinted at as worthy of notice, is this short passage in a treatise 

 De Significatione Cometarum: " Et nos invenimus modo quod apparuit intem- 

 pore nostro unus cometa in principio piscium, et cauda attigit usque ad princi- 

 pium geminorum in nocte Mercurii, et hoc fuit in ultimam noctem Junii, anno 

 499 Arab, et sequebatur ordinem signorum quousque venit usque ad principium 

 cancri, et dimisit ordinem signorum, et incepit deficere." 



The word Junii here found seems to have been transcribed by mistake for the 

 Arabic month Jumedi.j, the last day of which that year was Wednesday Feb. 7, 

 A. c. 1106; whereas the last day of June fell on a Saturday. This reading 

 agrees with the following notes concerning the same comet collected by Hevelius 

 in his Cometographia, p. 821. " a. c. 1106a prima hebdomada quadragesimae 

 cometam immensi fulgoris usque ad passionem Domini conspeximus." Lavath 

 ex Urspurg. — " a. c. IIO6, mense Februar. biduo post novilunium, visus est 

 magnus cometa, ad o<xasum solis brumalem." Calvis. ex Tyr. 



The new moon was Feb. 5, Ash- Wednesday that year Feb. 7, and Good- 

 Friday, March 23. 



If we suppose, with Dr. Halley, this comet to be the same with that which 

 appeared in 1 680, and that it was in perihelio Feb. 4, at noon (for it must have 

 been seen in 2 or 3 days after it had passed its perihelion) some of its places 

 would have been these: 



com. long. com. lat. 



Feb. 7^ 6" X 7° 50' 5° 44' north. 



March 14 7-1- y 1 1 49 



19 8 a 15 38 



24 8 a 19 2. 



The wide disagreement there is between the manuscript account of this comet, 

 and its places here computed, must very much lessen, if it does not quite over- 

 balance, the force of the arguments brought by Dr. Halley to prove the identity 

 of these two comets. Indeed if this comet had been the same with that of 

 168O, it could not have come to the beginning of Cancer, without a change in 

 the place of the perihelion too great to be easily admitted ; nor could it have left 

 the order of the signs without a change in the elements still greater. 



XLIV. Concerning the Effects of Lightning. By Mr. Franklin. Dated Phi- 

 ladelphia, June 10, 1751. p. 289. 



In captain Waddel's account (Phil. Trans. 492) of the effects of lightning on 

 his ship, Mr. F. could not but take notice of the large comazants (as he calls 

 them) that settled on the spintles at the topmast-heads, and burnt like very large 

 torches before the stroke. According to Mr. F.'s opinion, the electrical fire was 

 then drawing off, as by points, from the cloud; the magnitude of the fiame 



