350 
NATURE 
[FEBRUARY 7, 1907 
In the Journal of the Royal Microscopical Society for 
December, 1906, Dr. Alfred C. Stokes contributes a note 
on a certain form of butterfly scale the structure of which 
well illustrates certain points in connection with the much- 
studied ‘‘ Podura’’ scale. He says :—‘‘ These special 
wing-scales are formed of three distinct membranes, of 
which the upper and the lower bear longitudinal ribs, 
between which both membranes are distinctly, even con- 
spicuously perforated by minute apertures arranged in rows 
more or less horizontal.’’ It appears not to be generally 
known that the ‘‘ clouded yellow ’’ (Colias edusa) possesses 
pear-shaped wing-scales mixed with the ordinary scales, 
corresponding more or less closely to Dr. Stokes’s de- 
scription. These special scales seem to take the place 
of the ‘‘ plumules ’’ of many Pieridze and Satyride, and 
of the ‘‘ battledore ’’ scales of Lyczenide. 
Tue growth of the sudd on the Upper Nile, and the 
blocking of American rivers with plants of the water- 
fern, Azolla, are the danger 
arising out of the undue development of certain water 
weeds. The recorded from 
Australia, where Pontederia 
(Eichhornia) crassipes, bladder-like 
swollen petioles and attractive blue flowers, has, owing 
to its rapid propagation by means of offsets, become a 
nuisance in the northern rivers of New South Wales and 
in Queensland. A report prepared by the order of the 
Minister for Public Works in New South Wales discusses 
the origin of the plant, the methods and cost of eradi- 
cation, and proposes that a Noxious Weeds Bill should be 
introduced into Parliament. 
well-known examples of 
instance is 
hyacinth, 
characterised by its 
most recent 
the water 
THE report of the International Committee on Atomic 
Weights for 1907 is published in the current number 
(No. 319) of the Proceedings of the Chemical Society. 
New values are suggested, on the basis of determinations 
made during the past year, for bismuth, nitrogen, tantalum, 
and terbium, and the opinion is expressed that alterations 
are needed in the atomic weights of silver and chlorine. 
Before, however, recommending any change as regards 
these elements, the committee deems it advisable to wait 
for fuller information of the results of determinations 
known to be in progress, as the new values for silver and 
chlorine will have an influence on a large number of 
atomic weights. 
IN a paper on the relation of chemical activity to electro- 
lytic conductivity, by Mr. John L. Sammis, published in 
the Journal of Physical Chemistry (vol. x., No. 8), a large 
number of experimental observations are cited as disproving 
the views of Arrhenius and Ostwald that chemical activity 
in solution is proportional to the electrolytic conduction. 
The activity of acids in inverting sugar, catalysing esters, 
and dissolving magnesium is changed by the addition of 
benzene to the aqucous solution employed at a rate dis- 
proportionate to the conductivity. The replacement of one 
metal by another is said to take place in molten salts or 
solutions which are the best of insulators as well as in 
liquids which are good electrolytes. It was found that in 
sixty-nine non-conducting solutions of copper oleate pre- 
pared with different solvents, copper was easily precipi- 
tated by lead, whilst in fourteen other non-conducting 
solutions lead did not replace copper. The general purpose 
of the paper is to emphasise the view that the solvent is 
not indifferent to the solute. It is contended that the facts 
brought forward are explainable only on the hypothesis 
that ‘‘ chemical’? union between the solvent and 
the dissolved substance. 
NO. 1945, VOL. 75] 
occurs 
OUR ASTRONOMICAL COLUMN. 
ASTRONOMICAL OCCURRENCES IN FEBRUARY :— 
Feb. 8. 16h. Venus at greatest elongation, 46° 53’ W. 
»» 19h. Venus in conjunction with the Moon. Venus 
o 51’ N. 
g. 10h. Minimum of Algol (8 Persei), 
12, 6h. 49m. Minimum of Algol (8 Persei). 
15. 20h. Vesta in conjunction with the Moon, Vesta 
o° 42'S. 
19. 6h. 31m, to gh. 33m. Transit of Jupiter’s Sat. IIT. 
(Ganymede). 
20. 23h. Conjunction of Mercury and Saturn. Mercury 
1° 4o’ N. 
22. 6h, Conjunction of Jupiter with the Moon, Jupiter 
2° 45’ N. 
» 16h. 8m. to 16h. 58m. Moon occults y Geminorum 
(mag. 4°1). 
23. 7h. 11m. to 8h. 29m. 
(variable). 
25. 5h. 30m. to 6h. 31m. 
(mag. 4°2). 
26. toh. 12m. to 13h. 14m. 
(Ganymede). 
MicroMETER MEASURES DURING THE SOLAR ECLIPSE OF 
AuGust, 1905.—At the meeting of the Paris Academy of 
Sciences held on January 7, M. J. Merlin submitted a 
paper discussing the micrometer measures made at 
Roquetas (Spain) by MM. André and Guillaume during 
the total solar eclipse of August, 1905. From this dis- 
cussion he arrives at the conclusion that the lunar-parallax 
constant determined by Prof. Newcomb is not affected by 
any error sufficiently large to be detected by the measure- 
ments carried out. There is, however, room to correct 
the relative positions of the sun and moon as given in the 
Connaissance des Temps, although the correction does not 
modify the apparent trajectory of the moon in regard to 
the sun; it serves only to advance the position of the 
former in that trajectory by an amount corresponding to 
an advance of 11-1 seconds in the calculated times of the 
contacts (Comptes rendus, January 7). 
Moon occults ¢ Geminorum 
Moon occults 8 Cancri 
Transit of Jupiter's Sat. IIT. 
Hercnts oF MeEreors OBSERVED IN 1906.—In No. 4152 
of the Astronomische Nachrichten Mr. Denning gives the 
heights, lengths of paths, and velocities of ten large meteors 
observed in England during 1906. ‘The heights at the com- 
mencement of visibility varied from fifty-nine to eighty- 
nine miles, whilst those at disappearance varied from 
twenty-two to fifty-six miles. Seventy-two miles was the 
length of the longest path recorded, and twenty-four miles 
that of the shortest. The velocities determined lie between 
fifteen and thirty miles per second, the latter value having 
been determined for a Perseid observed on August 5, 
1906. 
A QuickLty CHANGING VARIABLE STAR.—In Bulletin No. 9 
of the Laws Observatory, University of Missouri, Mr. 
I’. H. Seares discusses the observations of the quickly 
changing variable star R.R. Draconis (188.1904) which 
were made at that observatory during 1905-6. The 
variable is of the Algol type, with a period of about 2-8 
days, and its light-curve is peculiar in being extraordinarily 
steep about the time of minimum. ‘The latter could not 
be determined exactly, because the star becomes invisible 
for about two hours in the 73-inch refractor employed, but 
the observations plainly showed that the range is greater 
than three magnitudes, and that the rate of change at 
the time of disappearance is one magnitude in half an 
hour. The normal magnitude of this object is 9-98, and 
the elements of its period, as determined from these observ- 
ations, are :— 
Min.=J.D. 2417026-682+2-831079d. E. G.M.T. 
Some of the residuals suggest the possibility of a variation 
in the period, but for the present this possibility remains 
very uncertain. 
Mercatr’s Comet 1906h.—Another set of elliptic elements 
for comet 1906h has been calculated by Mr. Crawford from 
observations made at the Lick Observatory. This gives 
October 5:66, 1906, as the time of perihelion passage, and 
8.23752 years as the period of the comet (Lick Observatory 
Bulletin, No. 108). 
