220 PHILOSOPHICAL TKANSACTIONS. [aHNO 175>. 



creased heat, and again lays it down at the command of the will, is the immediate 

 mechanical cause, by which the muscle does instantly contract, and is again re- 

 laxed, at the command of the will. 



^Tience it would appear that muscular voluntary motion is performed merely 

 as a sensation, (Hartley Conjecturae de Sensu, &c.) extremely acute, and under 

 the nicest management of the will ; which explains its velocity in a great measure. 



^LVllI. An Account of the Eruption of Mount Fesuvius, Jrom its first Be- 

 ginning to the 28th of October 1751, in a Letter from Mr. R. Supple, p. 315. 



TTiis communication is rendered unnecessary, 6rom a more particular account 

 being grven at p. !245 of this volume. 



XL IX. Of the Lunar Eclipse which happened Nov. 21, 1751 ; observed by Mr. 

 James Short, F. R. S. in Surry-street. p. 317. 



The weather was exceedingly tempestuous, and the sky overcast with clouds, 

 80 that the following times cannot be depended on to less than 2 minutes. 



Penumbra very visible at 7^ 58" 0» 



Beginning of the eclipse at. 8 6 O 



End of the eclipse at 11 6 O 



The quantity of this eclipse seemed about the middle to be larger than accord- 

 ing to all the tables. 



The Transit of the moon over the meridian. 



Preceding limb passed the meridian at 12'' 5" 18* 



Subsequent limb passed the meridian at 12 7 50 



Mr. Pound observed a similar eclipse at Wanstead, just two sarotic periods 

 before this, and has described it in the Philos. Trans. N° 347, and makes the 

 following remark, " This eclipse is the more considerable, as happening very 

 near the moon's perigee, and therefore usefld to veri^' her anomaly ; as also to 

 limit the greatest diameter of the shadow of the earth, and consequently the pa 

 rallax of the moon. This may be very properly compared with that of the 19th 

 of October 1697, whose middle was at 7"^ -Al" p. m. at London, and the quantity 

 the same as now." 



It may be added to Mr. Pound's remark above, that this eclipse happened 

 nearer to the moon's perigee, than that which he observed in the year 1715, 

 and therefore more proper for verifying the moon's anomaly, and limiting the 

 greatest diameter of the shadow of the earth. 



L. A Letter from the Reverend Father Augustin Hallerstein, of the Society of 

 Jesus, Pres. of the Astron. Col. at Pehin in China, to Dr. Mortimer, Sec. R. S. 

 Dated Pekin, Sept. 18, N. S. 1750. p. 31 9. 



This letter contains no real or usefiil information ; but only complaints of the 

 missionaries' vrant of means and instruments and information, &c 



