Aprin 23, 1914 
ton by Prof. C. G. Abbot, the retiring president, and 
reported at length in Science of March 6. The address 
forms a valuable apercu of the subject from Herschel’s 
pioneer actinometric observations down to the experi- 
ments made late last summer under the joint auspices 
of the Smithsonian Institution and the U.S. Weather 
Bureau on the employment of ballons-sondes in pyr- 
heliometric investigation. With regard to the solar 
constant, the mean value of 690 measurements made 
in connection with the Astrophysical Observatory of 
the Smithsonian Institution during the period 1902-13 
is stated to be 1-933 calories per sq. cm. a minute, a 
value which is probably accurate to 1 per cent. It 
will be noted that this period covers one sun-spot 
cycle, and it is also stated that the Mount Wilson 
measures indicate that the solar radiation is more 
intense at spot maximum than at minimum, the sun 
thus showing affinity with variable stars of the o-Ceti 
type. 
THE ACTION OF GRAVITY ON GaAsEOUS MIXTURES.— 
M. G. Gouy, in a recent communication to the Paris 
Academy of Sciences (Comptes rendus, vol. clviii., 
pp. 664-8) extends to the terrestrial atmosphere his 
researches on gaseous mixtures which during 1912 
led him to the conclusion that pressure could not be 
the cause of the general displacement of the Fraun- 
hofer lines towards the red. We may direct attention 
to the fact that the suggestion he then made that 
perhaps the explanation of this phenomenon would be 
found in the Doppler effect has received striking con- 
firmation on purely spectroscopic grounds very recently 
in the work of Mr. Evershed (Nature, March 10, 
p. 69). The present paper affords a mathematical 
demonstration of the impossibility of stratification 
according to density by the action of gravity on the 
gases in the earth’s atmosphere where the pressure 
exceeds that of a Crookes tube as the final result 
indicates that under these conditions the effect of 
gravity on the composition of the air is too slow to 
produce sensible effects. 
GROWTH AND CULTIVATION OF HOPS. 
TES close attention which is being given in many 
foreign countries to the scientific study of plants 
of economic importance is evidenced in the two reports 
on the hop lately published by Dr. J. Schmidt. 
Although the cultivation of hops in Denmark is at 
present restricted to about 100 acres, Dr. Schmidt, of 
the Carlsberg Laboratory, Copenhagen, was recently 
commissioned to visit this and other countries with 
the object of collecting information on the most 
modern methods of cultivation, and also to collect 
data and material likely to prove of value in the work 
of breeding improved varieties of hops for cultivation 
in Denmark. In t1910 the physiological department 
of the Carlsberg Laboratory began a series of inves- 
tigations on the hop plant (Humulus lupulus, 1.). 
with a view of obtaining information of theoretical 
and practical interest regarding this plant. These 
reports by Dr. Schmidt are the first-fruits of this 
work. 
In the first report, the growth in length of the 
stem and its diurnal periodicity is dealt with. One 
of the first problems for investigation that presented 
itself was to ascertain if the foreign varieties of hops 
obtained from southern regions which are being 
grown in the experimental garden attached to the 
Carlsberg Laboratory have a different rate of growth 
1 Johs. Schmidt: (:) ‘‘The Growth in Length of Hop-stems and its 
Diurnal Periodicity” (Comptes rendus des travaux du Lakoratoire de 
Carlsberg, rome vol., 2me livraison, 1913). 
Ident. (2) “The Rotational Movement of Hop-stems and its Diurnal 
Periodicity” (Z.c., 3me livraison, 1913). 
NOie32T, VOL. 94] 
NATURE 
199 
in the northern climate of Denmark from the wild- 
growing plant of that country. In the course of 
making these investigations, which are not yet con- 
cluded, the experiments detailed in this first report 
were made. 
Dr. Schmidt was at the outset inclined to the belief 
—a belief, by the way, which is firmly held by the 
practical hop-growers of Kent—that the growth of 
the hop stem, or “‘bine,’? would be strongest during 
the night. Observations on a number of plants soon 
showed, however, that the reverse is the case. The 
least growth took place during the six hours 9 p.m. 
to 3 a.m., which proved that darkness was not the 
dominant factor of growth. It might have been ex- 
pected that the growth-promoting factor of darkness 
, would first show itself as an ‘‘after-influence,’’ and 
that consequently the greatest growth would be 
during the following morning period, 3 a.m. to 9 a.m. 
_It was found, however, that the strongest growth 
occurred during the period 3 p.m. to 9 p.m., imme- 
diately preceding the darkest period, the value for 
the rate of growth increasing evenly from the mini- 
mum of the latter period to the maximum of the after- 
noon period. 
In the two main series of experiments, which were 
carried out in 1911 from the end of April, to the end 
of June, and in 1912 during July, the plants, growing 
in an unheated glasshouse, were kept as far as pos- 
sible under natural conditions. The measurements 
were made continuously at 6 o’clock in the morning, 
12 o’clock noon, 6 o’clock in the afternoon, and at 
12 o’clock at night. The diurnal oscillations of tem- 
perature were followed by means of a thermograph. 
Further experiments made seemed to show con- 
clusively that the influence of the temperature on the 
rate of growth under natural conditions predominates 
over the influence of humidity; as the author remarks, 
“the growth-promoting power, which high humidity 
is known to have under natural conditions, is 
‘covered’ by the influence of the temperature, so 
that it appears as if only the temperature was of 
any importance for the rate of growth of hop-stems.”’ 
The results of the investigations are summed up as 
follows :—‘‘ The growth in length of hop-stems under 
natural conditions has a very distinct diurnal period, 
the rate of growth being smallest during the night, 
greatest during the day. This periodicity is deter- 
mined by outer factors, among which the temperature 
has such a predominant influence that under natural 
conditions it determines the rate of growth.” 
The second report deals with investigations into the 
rotational movement of the hop-stem. In experiments 
with vigorous three-year-old hop-plants, in an un- 
heated glasshouse, the stems were found to show, 
during May and June, a rotational movement amount- 
ing on an average for one to two weeks’ observations 
to about 120° an hour, or one-third of the rate of the 
minute hand of the clock. The following table records 
the facts observed with two hop-plants, one (No. 14) 
obtained from Germany, the other (No. 36) from 
England :— 
No. of No. of No. of 
whole days Total rotation No. of turns in degrees 
under ob- __ in degrees turns 24 hours an hour 
servation (Average) (Average) 
Plant No. 14 es ey 
Shoot @... 9 24865 69 iY 115 
bids Obes 9 25875 72 re) 120 
seca C cece men 29810 83 Vas 113 
Plant No. 36 13 37600 104 80 120 
The rotational movement proved to have a very 
distinct daily periodicity, the rate being greatest 
during the day, least at night. This daily periodicity 
is determined by external factors, among which the 
temperature is of such dominating importance that 
