feb. 8, 1883] 
NATURE 
341 
are drawn on the sides of the platform so as to prolong 
the white lines on the sides of the magnetometer. By 
this means currents in amperes or potentials in volts can 
be at once read off without any calculation. 
The graduation of the current galvanometer may also 
be performed by means of electrolysis. The electro- 
chemical equivalents of a large number of the metals 
have been determined, and it is only necessary therefore, 
in order to graduate the instrument, to join it in series 
with a proper electrolytic cell and a constant battery, and 
to compare the amount of metal deposited on the negative 
plate of the cell with the total quantity of electricity 
which flows through the circuit in a certain time. A 
convenient cell may be made with two plates of copper, 
each about 50 square cms. in area, held parallel to one 
another about 2 cms. apart, and immersed in a nearly 
neutral solution of copper-sulphate in a glass beaker. A 
current of one ampere through sucha cell gives a very good 
result. This current will deposit about 1'2 grammes of 
copper per hour, which, when light plates are used, can 
be very accurately weighed. The plates should be care- 
fully cleaned, dried, and weighed before being immersed 
in the liquid, and care must be taken not to send the 
current through the cell at all until it is made to flow 
continuously for the experiment. The instant the current 
through the cell is completed should be noted, and 
readings of the current galvanometer taken at equal 
short intervals during the time allowed for the experi- 
ment. The average of these readings is to be taken as 
the average reading of the galvanometer. When the 
experiment has been completed the plates are to be 
taken out and very carefully washed in clean water and 
dried before being weighed. It is generally better to 
calculate the quantity of electricity from the gain of the 
negative plate than from the loss of the positive. The 
electro-chemical equivalent of copper has been recently 
determined afresh with great care in the Physical 
Laboratory of the University of Glasgow by Mr. Thomas 
Gray, and as the result of his experiments ‘000331 of a 
gramme of copper is deposited by the passage of one 
coulomb of electricity. Dividing the gain of weight of 
the negative plate by this number, we obtain the total 
number of coulombs which have flowed through the 
galvanometer during the experiment. This divided by 
the time in seconds gives the average current in amperes ; 
from which the number corresponding to the position of 
the magnetometer on the platform can be determined, 
and the graduation completed in the manner described 
above. 
Errata in Part II. of this Article—P. 106, line 2 from 
top, for 2r7zCA read 2CA; line 5, for CD(=+) read 
CD(= y) ; line 6, for DE (= y) read DE(=+). 
ANDREW GRAY 
NORWEGIAN GEODETICAL OPERATIONS? 
ais publication of the Norwegian Committee of the 
Association for the Measurement of Degrees in 
Europe is a report of the observations made at two 
tidal stations in Norway—Oscarsborg and Drontheim. 
The report opens with a summary of the previous tidal 
operations carried out in Norway. From June 8 to 28, 
1835, a series of observations were made at a large num- 
ber of stations at the request of the English Admiralty. 
These observations, together with those from numerous 
other stations in Europe, along the North Sea, and 
Atlantic coasts, were reduced and compared by the Rev. 
Dr. Whewell, and were published by him in the P/z/o- 
sophical Transactions of 1836. 
The next tidal operations recorded were undertaken in 
1839, to ascertain whether, as supposed, the Norwegian 
coast is slowly rising. With this object, marks were cut 
* Publication of the Norwegian Committee of the Association for the 
Measurement of Degrees in Europe, Part I. (Christiana, 1882.) 
in the rock at twenty-six points along the coast, and the 
date was inscribed in each case. On the eastern coast, 
where there is little or no tide, only one mark was cut, at 
the level of the water; but along the western and northern 
coasts two marks were made, one at high water, and the 
other at low water. The report gives a detailed descrip- 
tion of the position of these marks. In 1865 observations 
were made to ascertain if any alteration had taken place 
in the relative positions of these marks and of the sea, 
and it was found that on an average the land was rising 
at the rate of 3” in 26 years. It was, however, seen that 
such determinations were very inadequate, since the mean 
level of the sea had not been taken into account, and the 
marks were not connected by lines of levelling. The 
whole question was accordingly placed before a Com- 
mittee of the University. This Committee, however, 
came to no conclusion, principally on the ground of the 
expense of the necessary levelling operations. It was 
then pointed out by Prof. Fearnley, the chairman of the 
Committee of the Association for the Measurement of 
Degrees in Europe, that the resolutions of the Association 
at the General Assembly in 1864, at Berlin, had given an 
increased importance to the determination of the mean 
tide level. Nevertheless, it was not until 1876 that any 
steps were taken to establish a series of tidal stations 
provided with self-registering apparatus, as enjoined by 
the Association ; six stations have now been established, 
and two more are to be formed. 
Previously however, namely, in 1872, two stations had 
been established, one at Oscarsborg, in the fortified 
island of Kaholmen, situated in the Christiana fiord, 
in connection with submarine mining, and where ob- 
servations have been recorded from 1872 to 1879; the 
other at Drontheim in connection with the harbour 
works, the observations at this station have extended 
from 1872 to 1878. These two sets of observations form, 
as already mentioned, the subject of the present report. 
At both stations self-registering apparatus of simple 
designs were used. At Oscarsborg the rise and fall of 
the tide was marked on a P/ave sheet of paper attached 
to a frame moving horizontally. The motion was im- 
parted to this frame by a weight, which, in order that the 
motion might be uniform, was connected to a clock. 
The float was inclosed ina tube, so as to annul the dis- 
turbing action of the waves. At Drontheim the paper 
was attached to a drum rotating uniformly by means of 
clock-work. The apparatus was placed at the end of a 
pier, and the scribing pencil was connected by a system 
of rods to a bridge, the other’end of which was supported 
by a pontoon. In this manner the action of the waves 
was eliminated. The mean tide level was obtained at 
these two stations by taking the arithmetic mean of the 
heights of the tide recorded on the diagrams for each 
hour, and not by the more accurate method based on the 
areas described. But since these observations extended 
over several years, the result is no doubt practically the 
same; moreover, neither apparatus was provided with 
any means of obtaining the areas automatically, and to 
calculate them would have involved an enormous amount 
of labour. 
The observations at both stations are arranged in a 
series of tables.’ Table I. gives the heights of the tide 
at each hour, commencing at noon, for every day during 
one month.* The arithmetic mean of the heights of the 
tide at the same hour each day during the month, are 
also given for every hour of the day; the moon’s in- 
fluence does not appear in these means, they therefore 
show the influence of the sun. These means, for every 
month during which the observations lasted, are collected 
together in Table IV., and the mean of these means is 
also given. Table II. gives the height of high and low 
* The corresponding tables in each set of observations are denoted by the 
same number. 
2 This table was not extended further, in order to save space in the 
Report. 
