512 

Atlantic, and Gulf coasts the lines show a distinct 
tendency to be parallel to the sea-coast. The 
distribution is chiefly controlled by temperature, 
direction of prevailing winds, distance, and direction 
of the chief source of moisture supply, and general 
topography. Charts given with the communication 
are taken from the ‘ Atlas of American Agriculture.” 
A belt of uniformly high relative humidity along the 
coasts averages about 75-80 per cent., and at times 
exceeds 90 per cent. on the Pacific coast. Inland, in 
parts, the minima relative humidity during the hot 
summers fall to 30 per cent., and even 20 per cent. 
over the districts of most extreme aridity. Absolute 
humidity, which shows the actual amount of water 
vapour in the air expressed in decimals of inches, and 
known as vapour pressure, is also dealt with; two 
charts are given showing the equal pressure lines over 
the United States in the months of January and July. 
Temperature is essentially the chief control of 
absolute humidity ; in mid-summer the amount of 
moisture in the atmosphere is generally from two to 
four times as great as in mid-winter. 
GEOLOGY AND THE IcE-cAP IN NORTHERN GREEN- 
LAND.—The interest of Dr. Lauge Koch’s geological 
mapping in Northern Greenland (NATURE, vol. IIo, 
Pp. 91) is now increased by his preliminary account of 
Peary Land. His new map (Am. Journ. Sci., vol. 
206, p. 190, 1923) shows the continuation of the 
Caledonian folding through the north of the region, 
where moraine-matter from the glaciers descending 
from the south obscures much of a country in any 
case difficult forresearch. The ice-cap extended a good 
deal farther north at the maximum of the Pleistocene 
ice-age, but did not cover all the coastland. It may 
be remarked that in this area we have once more 
evidence of the potency of snow-domes in promoting 
widely spread glaciation. It seems unnecessary, if 
unfashionable, to shift the pole to account for every 
local centre of ice-radiation. The main result of 
Lauge Koch’s recent work is the discovery of a richly 
fossiliferous Ordovician series far greater in extent 
and thickness (870 m.) than he could anticipate when 
he began his arduous explorations in 1917. 
PRODUCTION OF LEAD IN Britain.—In the numbers 
of Chemistry and Industry for March 16 and 23, Prof. ; 
H. Louis contributes a most interesting and valuable | 
account of the production of lead in Britain. He 
begins with a clear account of lead in ancient times. 
The first definite mention of the production of lead 
in Britain occurs in Pliny (a.D. 77) ; a pig of lead has 
been found in the Mendip Hills bearing the name of 
the Emperor Claudius (A.D. 49), and in A.D. 64 
smelting in Flintshire began. Some pigs of Roman 
lead are stamped ex arg., 1.e. desilvered—probably by 
cupellation. The progress made in the Middle Ages 
is described in detail by Prof. Louis, whose articles 
have a wide interest. 
SUBSTITUTION IN THE BENZENE NucLEeus.—In the 
Chemical News of March 16, Messrs. R. Fraser and 
J. E. Humphries discuss the problem of substitution 
in the benzene nucleus in the light of the Lewis- 
Langmuir theory of co-valence. They start from 
three simple postulates related to the octet stability 
of an atom or group, and discuss in an interesting 
manner many known results in organic chemistry. 
In the chaotic mass of unco-ordinated facts which 
lies heavy on organic chemistry a ferment is evidently 
moving ; in time the material will no doubt be brought 
into order, and discussions of the type of that 
mentioned cannot fail to be of service in this direction. 
_Earty History oF THE Gas Process.—The early 
history of the manufacture and distribution of towns’ 
gas was briefly outlined by Mr. D. Brownlie in a paper 
NO. 2789, VOL. 111] 
eden URE 


[APRIL 14, 1923 
read before the Newcomen Society on March 20. 
Van Helmont, in 1600, observed that “‘ coal did belch 
forth a wild spirit or breath.’’ Other early pioneers 
include Thomas Shirley (1667), Robert Boyle (1691), 
Stephen Hales (1726), J. Clayton (1739), Bishop Watson 
(1781), the Earl of Dundonald (1781), and Minckelers 
(1784). William Murdoch lighted his house at 
Redruth with coal gas in 1792. At first the gas was 
burned at the open end of an iron pipe, but the 
accidental use of an old thimble led to the introduction 
of a burner in which the gas was lit at a number of 
jets issuing from a perforated thimble. Messrs. 
Boulton and Watt’s works at Soho, Birmingham, 
were illuminated by gas in 1802. The plant erected 
by Murdoch for this purpose differed in little but 
scale from the horizontal settings and gasometers of 
to-day. Lebon, in France, worked along much the 
same lines as Murdoch, and illumined his house with 
coal gas in 1801. Winsor illumined part of Pall 
Mall with gas in 1807. Samuel Clegg introduced 
lime purification in 1806, and invented the first gas- 
meter in 1815. In the early days gas was distributed 
through lead or wood pipes. Cast-iron pipes were 
introduced in 1810, and wrought-iron pipes in 1825. 
John Grafton, in 1820, introduced the use of fireclay 
instead of iron for retorts. This permitted the tem- 
perature of carbonisation being raised from 1400° F. 
to 2000° F. Clegg patented- retorts for continuous 
carbonisation in 1815. The first vertical gas retort 
was patented in 1828 by John Brunton. 
PHOTOMETRY.—In his annual address before the 
Philosophical Society of Washington, the retiring 
president, Mr. E. C. Crittenden, presented an in- 
teresting survey of problems involved in the measure- 
ment of light. The address has appeared in the 
Journal of the Washington Academy of Sciences 
(vol. 13, No. 5, March 4, 1923). In the introduction 
Mr. Crittenden recalls several notable advances in 
photometry, such as the adoption of the international 
unit of candle-power by all leading countries except 
the Germanic nations. In view of the uncertainties 
attending the use of flame standards, this unit is 
now usually preserved by the aid of calibrated electric 
incandescent lamps ; the process is analogous to that 
adopted for the international ohm, derived from a 
mercury standard but maintained by means of wire 
resistances. However, there is this important dis- 
tinction, that we have as yet no adequate, accurate, 
and reproducible primary standard of light. One of 
the most hopeful lines of investigation is that pursued 
at the U.S. Bureau of Standards, where experiments 
on a black body maintained at a definite temperature 
have been made; the black body takes the form of 
a carbon-tube electric furnace matched in colour by 
comparison with certain standard incandescent lamps. 
But further information on the accuracy with which 
temperature can be maintained is needed. The 
address also directs attention to the fundamental 
distinction between conceptions of light as radiation, — 
and as a physiological impression—a distinction that 
becomes specially important when we have to deal 
with’ sources yielding light of different colour. The 
physiological phenomena affecting such comparisons 
are discussed, and some remarks are made on the 
results of ‘‘ equality of brightness’’ and “ flicker 
photometer ’’’ measurements. The visibility curve, 
throughout the spectrum, of the normal eye has now 
been ascertained with fair precision. A knowledge 
of this should. enable us to evaluate the luminous 
power of any variety of radiant energy; and if, in 
addition, the primary standard based on the black 
body at specified temperature should prove satis- 
factory, considerable progress towards the scientific 
measurement of light will have been made. 
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