| Sept. 16, 1886] 
sold by the British Association, 22, Albemarle Street, W. The 
Indian tidal results of all previous years, and those given in the 
various reports to the British Association, have been reduced by 
Major Baird to the standard form recommended in the report of 
1883. To these have been added the results derived by the 
United States Coast Survey, and the whole has been published 
in the Proceedings of the Royal Society, No. 239, 1885, in a 
paper by Major Baird and Prof. Darwin. In the course of the 
Indian tidal operations a discussion has arisen as to the deter- 
mination of a datum-level for tide-tables. The custom of the 
Admiralty is to refer the tides to ‘‘ the mean low-water mark of 
ordinary spring tides.” This datum has not a precise scientific 
meaning, as the diurnal tides enter into the determination of the 
datum in an undefined manner; and it follows that two determin- 
ations, both equally defensible, might differ sensibly from one 
another. A datum-level should be sufficiently low to obviate 
the frequent occurrence of negative entries in a tide-table, and 
it should be rigorously determinable from tidal theory. It is now 
proposed to adopt as the datum-level at any new ports in India, for 
which tide-tables are to be issued, a datum to be called ‘‘ the 
Indian spring low-water mark,” and which is to be below mean 
sea-level by the sum of the mean semi-ranges of the tides My, 
S., Kj, O; or, in the notation used below,— 
H,, + H, + H’ + Ho 
below mean water-mark. This datum is found to agree pretty 
nearly with the Admiralty datum, but is usually a few inches 
lower. The definition is not founded on any precise theoretical 
considerations, but it satisfies the conditions of 2 good datum, 
and is precisely referable to tidal theory. If, when further 
observations are made, it is found that the values of the several 
H’s require correction, it is not proposed that the datum-level 
shall be altered accordingly, but, -when once fixed, it is to be 
always adhered to. The report then shows how harmonic 
analysis might be applied to the reduction of a short series of 
tidal observations, such as might be made when a ship lies for 
a fortnight or a month ina port. ‘The method has been applied 
by Mr. Alnutt to the computation of tide-tables at Port Blair 
and several other ports, and the computed results are compared 
with those given both by a rigorous instrument and by actual ob- 
servation. It is remarked that, while better agreement was to be 
desired, the errors are inconsiderable fractions of the whole in- 
tervals of time and heights under consideration. An attempt 
made to detect the ninmeteen-yearly tide by observations at 
Karachi has led to the belief that it is extremely improbable 
that this important datum will ever be detected. 
P. T. Main presented a Report on our Experimental Know- 
ledge of Certain Properties of Matter.—Vhe report discussed 
recent work on the testing of Boyle’s law for very low as well as 
for very high pressures, the researches of Amagat and C. Bohr 
being included. It then passed to the verification of Gay-Lussac’s 
law. Recent researches on the saturated pressures of vapours at 
various temperatures, especially those of Ramsay and Young, 
were next considered, especially to determine (1) whether 
statical and dynamical methods of observation lead to similar 
results ; (2) whether the pressures of ice and of water-vapour are 
the same at the same temperature. The important question of 
the pressure of mercury-vapour, and modern research in the 
determination of the critical points of nitrogen and other gases, 
and in the measurement of vapour-densities, were also included. 
Prof. George Forbes presented the Report of the Committee 
on Standards of Light.—Yhe Committee had met repeatedly 
during last winter. It had been proposed in last year’s report to 
carry on experiments on electrical standards in the hope of 
arriving at an absolute standard of light. One of the first steps 
was to discover a means of reproducing a definite temperature, 
and certain experiments were proposed for this purpose. At one 
of the first meetings of the Committee Capt. Abney announced 
that he had already found a means of doing this in a different 
manner to that proposed in the Committee’s report, and depend- 
ing only upon the change of resistance of the carbon filament. 
Under these circumstances the Committee left this part of the 
experimental investigation to be reported upon by Capt. Abney. 
His further researches had, however, led him to believe that the 
law which he had announced to the Committee did not hold with 
all qualities of carbon filament. He had, however, been engaged 
upon further experimental researches, which were almost ready 
for publication, and which had an important bearing upon the 
labours of the Committee. In last year’s report attention was 
NATURE 
479 
drawn to the value of the pentane standard of Mr. Vernon 
Harcourt as a practical reproducible standard, and Mr. Rawson 
had been since then engaged in a further examination of that 
standard. Sir James Douglass had also made some experiments 
which were not quite completed, but had-gone so far as to give 
great promise. Some account of the experiments in that report 
had been expected by the Committee, but the absence of Sir 
James Douglass on official business had interfered with this. At 
one of the first meetings of the Committee the Secretary showed 
what he had done in the way of improving thermopiles such as 
it was hoped would be of use in the investigations recommended 
in last year’s report, and he was instructed by the Committee to 
proceed with the construction of the instrument, which had been 
completed, and was now to be placed before the Section and 
described in a separate paper. The Committee requested to be 
re-appointed, with a grant of 25/. 
Report of the Committee on Electrolysis, presented by Prof. 
Oliver J. Lodge (Secretary).—The report, which was only an 
interim report, stated that only one meeting had been held, but a 
large amount. of correspondence had passed, as well as work 
done by the various members. This work was discussed in 
separate papers. The Committee asked to be re-appointed with 
a grant to defray the expense chiefly of printing selected memoirs, 
and of getting pure substances. 
Report of the Committee on English Channel Tides.—The 
Committee had received the records of the self-recording tide- 
gauges at Dover and Ostend for the four years 1889 to 1883. 
These are so bulky that they content themselves with discussing 
in an appendix to the report the records of four periods of a 
fortnight in the year 1883, namely, at the solstices and the equi- 
noxes. Of these diagrams were shown. The Committee suggest 
that they hand over their papers and records to the Committee 
for the Harmonic Analysis of Tides. 
Prof. Johnson submitted the Report of the Committee formed 
in Canada to establish a System of Tidal Observations im that 
Country.—He said they had communicated with the Government 
in the matter, and while, owing to the expense at present incurred 
in hydrographical work on Lake Ontario and elsewhere, the 
Government had not yet given their consent, it was hoped that 
before long their object would be attained. The Committee 
asked for re-appointment. 
Report of the Electrical Standards Committee, presented by 
Mr. Glazebrook (Secretary).—Eighteen standard coils have been 
tested during the year, and certificates of their value is-ued. 
The attention of the Secretary was called to the fact that the 
paraffin in some of the coils showed a trace of green coloration 
round the edges. This has been shown to arise from the action 
of a small amount of acid, left in the paraffin, on the copper of 
the case and connecting-rods, and the Committee are considering 
how to deal with the difficulty. At present the insulation resist- 
ance of the coils is extremely high, amounting t» as much as 
8000 megohms. The Committee wish to express their sense of 
the great desirability of establishing a National Standardising 
Laboratory for Electrical Instruments on a permanent basis, 
and their readiness to co-operate in the endeavour to secure the 
same. The Committee apply forre-appointment, with the addition 
of the name of Mr. J. T. Bottomley. 
Second Report on the Fossil Plants of the Tertiary and 
Secondary Bids of the United Kingdom, by F S. Gardner.— 
Attention has been devoted exclusively this year to the fossil 
flowering or phanerogamous plants. The results point to the 
conclusion that while the Gymnosperms, to which the Coniferae 
belong, are of the highest antiquity, there are no angiospermous 
plants in British rocks older than the Secondary, if we except 
the problematic plant known as Sférangium. Even so late as 
the Lias no indisputable Angiosperm has been discovered within 
our area, for the supposed Monocotyledons from the Rheetics, 
near Bristol, hitherto referred to the fa.nily of ’ond-weeds under 
the name Wajadita, are really cryptogamic plants of the moss 
tribe, closely allied to the river moss Fortmadis. This group 
had not previously been found fossil, and, so far as it goes, would 
indicate rather a temperate climate. It is important to notice 
that these conclusions are shared by Prof. Williamson, Mr. 
Carruthers, and by all botanists who have examined them, as 
well as by Mr. Brodie, the possessor of the specimens. The 
Lilia, Bensonia, and other supposed Monocotyiedons of similar 
age are very imperfectly preserved, and doubtless referable to 
Cycads, a family which abounded then. 
