548 Proceedings of the Poyal Society 
despised. The number of such stars is great, the number of 
observers small. 
Next in order comes the size and shape of the earth. A rela- 
tively small difference in our position on the earth’s surface makes 
a notable difference on the apparent position of the moon, and, in 
consequence, on the time of the occultation ; even the height of the 
observer above the level of the sea has its influence. This may 
be well studied in the present instance ; viewed from our latitude, 
the moon was seen to pass a little to the south of the planet Mars, 
whereas in the southern counties of England an occultation was seen. 
The oblateness of the earth has also to be taken into account. In 
the present instance calculations made as if the earth were spherical, 
would give the disappearance Some eighteen seconds earlier than the 
above. Hence observations made on these phenomena from places 
in different latitudes afford a means for determining the earth’s 
oblateness. 
But, lastly, these observations are all deranged by the extreme 
jaggedness of the moon’s edge. This jaggedness is well seen during 
an eclipse of the sun ; it is also conspicuous against the disc of a 
planet. I recollect of witnessing an occultation of Saturn, some 
half a century ago, during which the corner of a lunar mountain was 
projected against the planet in such a way as to cut out a sector of 
about one-third of the surface. Irregularities of such magnitude 
cause serious variations in the times of disappearance and reappear- 
ance ; and, for the purpose of estimating their possible extent, it 
might be useful to make concerted observations at places a few 
miles apart, so that the appulse may happen, here on the top of a 
lunar mountain, there in the hollow. 
2. On Currents produced by Friction between Conducting > 
Substances, and on a new form of Telephone Receiver. 
By James Blyth, M.A. 
In former papers laid before this Society, I showed that when 
any two metals are rubbed against each other, a current of electri- 
city is produced ; and that this current agrees in direction with the 
thermo-electric current for the same two metals, and is greater, 
approximately at least, in proportion as the metals rubbed are far 
