18 
NATURE 
[May 4, 1871 
OE rr 
needle or of resistance scales. It consists of two voltameter 
tubes fixed upon graduated scales, which are so connected that 
the current ofa battery is divided between them, with one branch 
including a known and permanent resistance, and the unknown 
resistance to be measured. The resistance and polarisation being 
equal, and the battery being common to both circuits, these un- 
stable elements are eliminated by balancing them from the cir- 
culation, and an expression is found for the unknown resistance 
X in the known resistances C and y of the voltameter, including 
the connecting wires and the yolumes V and V’ of gases evolved 
in an arbitrary space of time within the tubes, viz. :— 
(1) 
Changes of atmospheric pressure affect both sides equally, and 
do not therefore influence the results; but a reading of the at- 
mospheric pressure is obtained at both sides by lowering the 
little supply reservoir with dilute acid to the level indicated in 
the corresponding tube. The upper ends of the voltameter tubes 
are closed by small weighted levers provided with cushions of 
india-rubber ; but after each observation these levers are raised, 
and the supply reservoirs moved so as to cause the escape of the 
gases until the liquid within the tubes is again brought up to the 
zero line of the scale, when the instrument is ready for another 
observation. A series of measurements are given of resistances 
varying from I to 10,000 units, showing that the results agree 
within one per cent. with the independent measurements obtained 
of the same resistances by the Wheatstone method. 
The advantages claimed for the proposed instrument are, that 
it is not influenced by magnetic disturbances, or the ship's 
motion if used at sea; that it can be used by persons not 
familiar with electrical testing ; and that it is extremely simple 
and easily procured. 
Royal Institution of Great Britain, Annual Meeting, 
Monday, May 1.—Sir Henry Holland, Bart., F.R.S., president, 
in the chair. The Annual Report of the Committee of Visitors 
for the year 1870 was read and adopted. Eighty-one new 
members were elected in 1870. Sixty-three lectures and nineteen 
evening discourses were delivered during the year 1870. The 
books and pamphlets presented in 1870 amounted to I 18 volumes, 
making, with those purchased by the managers, a total of 307 
volumes added to the library in the year, exclusive of periodicals. 
Thanks were voted to the president, treasurer, and secretary, to 
the committees of managers and visitors, and to the professors, 
for their services to the Institution during the past year. The 
following gentlemen were unanimously elected as officers for the 
ensuing year: President—Sir Henry Holland, Bart., F.R.S. 
Treasurer—Mr. William Spottiswoode, F.R.S. Secretary—Dr. 
Henry Bence Jones, F.R.S. Managers—Mr. John J. Rigsby, 
F.R.S., Mr. George Berkley, Mr. William Bowman, E.R.S., 
Mr. George Busk, F.R.S., Mr. Warren De la Rue, F.R.S., 
Capt. Douglas Galton, C.B., F.R.S., Mr. John Hall Gladstone, 
F.R.S., Mr. William Robert Grove, F.R.S., the Lord Lindsay, 
Mr. George Macilwain, the Duke of Northumberland, William 
Pole, F.R.S., Sir W. Frederick Pollock, Bart., Mr. Robert 
P. Roupell, Col. Philip James Yorke, F.R.S. 
Geological Society, April 5.—Prof. Monis, vice-president, 
in the chair. The following communications were read :—I. 
«* On a new Chimeroid Fish from the Lias of Lyme Regis,” by 
Sir Philip Grey Egerton, Bart., M.P., F.RS. The fish for which the 
author proposed the name of Ischyodus orthorhinus, was repre- 
sented by a specimen showing the anterior structures imbedded 
in a slab of Lias. It exhibited the characteristic dental apparatus 
of the Chimzeroids, surrounded with shagreen, a very large pre- 
labial appendage six inches long, and terminating in a hook 
abruptly turned downwards, and a process which the author re- 
garded as representing the well-known rostral appendage of the 
male Chimzroid, but in this case attaining a length of 53 inches, 
and covered more or less thickly with tubercles, bearing recurved 
central spines somewhat toothlike in their aspect. This appen- 
dage is attached to the head by a rounded condyle, received into 
a hollow in the frontal cartilage. The dorsal spine, which mea- 
sured 6 inches in length, was articulated by a rounded surface to 
a strong cartilaginous plate projecting upwards from the noto- 
chordal axis, and was thus rendered capable of a considerable 
amount of motion ina vertical plane. This structure also occurred 
in Callorhynchus and Chimera. Dr. Giinther commented on the 
interest of this discovery, as in no other sharks is the same articu- 
lation of the dorsal spine as that described in the paper to be 
found, He inquired whether the granulated plate supposed to 
x= C+ = (cee o 
vy | Y) Y 


be dorsal might not be a part of the armature of the lateral line, 
as in sturgeons. He thought that the Chimeroids would even- 
tually prove to be intermediate between the ganoid and shark 
types, and that all belonged to one subclass. Mr. Gwyn Jeffreys 
inquired what other remains were found with these fishes such as 
might represent the food, molluscan or otherwise, on which they 
lived. Sir P. Egerton replied that there was no deficiency of 
pabulum for any kind of fish in the sea represented by the Lias 
of Lyme Regis. He also made some remarks on another some- 
what similar specimen in his own museum. The plate referred 
to by Dr. Giinther, he stated, was symmetrical, and not like the 
lateral plates on the sturgeon, which are unsymmetrical. He 
therefore thought it dorsal.—2. ‘* On the Tertiary Volcanic Rocks 
of the British Islands,” by Archibald Geikie, F.R.S. In this 
communication the author gave the first of a series of papers 
which he proposes to lay before the society upon the volcanic 
rocks of Britain of later date than the chalk. In a general intro- 
duction to the whole subject, he pointed out the area occupied by 
the rocks, showing that they are chiefly developed along the broad 
tract which extends from the south of Antrim, between the chain 
of the Outer Hebrides and the mainland of Scotland, up into 
the Faroe Islands, and even to Iceland. The nomenclature of 
the rocks was discussed, and the following arrangement was 
proposed :— 








i = 
Felspathic series || Pyroxenics | 
pathic series | or Augitic. 
[2 |é all fe 
[2 [Fe lal@ 
1O |o > Lees 
=e Sslisis2 
3 4 8/5/52 
=) Bs - OUIlF/5a 
5 ¢ Sallbl. s 
| Pl ol als e/2Zielos 
Jone Sl sre =|S8isre8 
Bifsis e| |2les5isle 
2) Ss ale2ls\Plels/b esiales 
S\SCE SS 4) 5 S\5 85 atm 
it oe \eQl Ora lOl= Si nie 
o|4 SSiSolsolealalaaia = w 
Si AH SOS) ol/ Ol al Ela~ ose 
As F AIA RIA A 
= SS s 
I. INTERBEDDED OR CONTEM- 
PORANEOUS. 
A. Crystalline. 
Sheets or beds cssccscseesssseees|ace| ave | 2 | *|*|]/*]* [ee] * 
B. Fragmental. 
Beds or layers sssessssasaceneces| cel) ose | soa [avz|ao |] aaefece foun) caenl || SINE 
II. INTRUSIVE OR SUBSEQUENT. 
A. Crystaliine. 
a. Amorphous masses *| * | 
B. Sheets.. = * 
y. Dykes * *|* 
3. Necks ... ? i) 
B. Fragmental 
Neecks..ceceseeccecceee * 













The age of the rocks was shown to be included in the Tertiary 
period by the position of the volcanic masses above the chak, 
and by their including beds containing Miocene plants. As 
an illustrative district, the author described the . volcanic 
geology of the island of Eigg, one of the Inner Hebrides, and 
brought out the following points:—1. The volcanic rocks of 
this island rest unconformably upon strata of Oolitic age. 
2. They consist almost wholly of a succession of nearly horizon- 
tal interbedded sheets of dolerite and basalt, forming an isolated 
fragment of the great volcanic plateau which stretches in broken 
masses from Antrim through the Inner Hebrides. 3. These 
interbedded sheets are traversed by veins and dykes of similar 
materials, the dykes having the characteristic north-westerly 
trend, with which they pass across the southern half of Scotland 
and the north of England. Veins of pitchstone and felstone, 
and intrusive masses of quartziferous porphyry, like some of those 
which in Skye traverse or overlie the lias, likewise intersect the 
bedded dolerites and basalts of Eigg. 4. At least, two widely 
separated epochs of volcanic activity are represented by the 
volcanic rocks of Eigg. The older is marked by the bedded 
dolerites and by the basalt veins and dykes which, though strictly 
speaking younger than the bedded sheets which they intersect, 
yet probably belong to the same continuous period of volcanic 
action. The later manifestations of this action are shown by the 
pitchstone of the Scur. Before that rock was erupted the older 
doleritic lavas had long ceased to flow in this district. Their 
successive beds, widely and deeply eroded by atmospheric waste, 
were here hollowed into a valley traversed by a river, which 
carried southward the drainage of the wooded northern hills. 
Into this valley, slowly scooped out of the older volcanic series 
