yan. 



L004J 



NA TURE 



7 



From these curves were deduced the mi::i'ii 

 I , II., III. in C.G..^. u.iits. 



Table I. — Tiuo Disks 



;;iven in Tables 



Table II. — A Paraboloidal Point and a Disk 



Table III. — Two ParaboloiJa' Points 



Au inspection of the diagram, drawn on a reduced scale from 

 the carves as orioinally laid down, bhows that the curve for 

 approximate planes (slightly cor.ve.v, to 11. sure the centres being 

 the most prominent) is continuously concave, whereas those for 

 both point and disk and two points are concave only for a certaui 

 di>t"nce, and then turn off and become convex. Moreover, it is seen 

 that the intensity of force per centimetre decreases continuously up 

 to 15,450 volts in the case of planes ; but that, in the case of a 

 point and disk, and also in that of two points, the decrease 

 ceases after a certain potential has been reached, and that then 

 it increases so as to become nearly a constant quantity. Between 

 a point and a disk the potential per centimetre at 9,000 volts 

 and beyond is very nearly 9,200 ; consequently, if tlie law holds 

 gool, to produce a spark I decimetre (3-94 inches) long, 92,000 

 volts, one I metre (39-37 inches) long, 920.000 volts,' and a 

 flash of lightning i kilometre (0-621 mile) in length, a potential 

 of 920,000,000 volts would be required, but this potential would 

 be lessened by the diminution of the atmospheric pressure at the 

 height of a kilometre, namely 607-4 ™>^- (799. 210 M), or a 

 mean pressure of 713-8 mm. (939,211 M) between i kilometre 

 and the earth. Taking the mean pressure 939,211 M, it would 

 require 864,000,000 volts to produce a discharge between a cloud 

 (regarded as a point) i kilometre high and the earth. 



It is extremely dilircult to conjecluie how a cloud can become 

 charged to such au enormous potential, unle.-s the charged mole- 

 cules balance each other (as those of a stratum in a vacuum tube 

 may be conceived to do) until a di-turbing cause breaks up the 

 arrangement ; and then the whole of them are discharged in one 

 dii-ection with their aggregate potential. 



We may add that less than 15,000 cells would not have sufficed 

 to make out the fact that the intensity of force to produce a dis- 

 charge between a point and disk or two points becomes a 

 constant after 9,oco to 11,000 celK has been reached. 



The following table gives the ratios of the striking distances 

 between a point and a disk and two points respectively, taking 

 those between two disks as unity. And also the relation belween 

 the striking distances between a point and a disk and between 

 two points, taking those between a point and a disk as unity. 



Tha saiking distainces from which the above ratios are calcu- 

 lated are those obtained from the smoothed curves. 



January 17. — "Evidence of a Large Extinct Australian Lizard 

 (Notiosaurus dentatus, Ow.)," by Sir Richard Owen, K.C.B., 

 F.R.S., &c. 



This evidence is based on a small fragment, seemingly of coal, 

 with roots of two teeth adherent thereto, transmitted to the author 

 from the Department of Mines, Sydney, New South Wales ; 

 bnt stated to be from a Pleistocene deposit. The author had 



^ To produ 



nple 



