342 
NATURE 
[Aug. 28, 1873 
ring in their indications ; some going well so long as a 
small range of pressure is recorded, but undergoing altera- 
tions after every great barometrical depression; some 
constantly altering in one direction, others in either direc- 
tion, &c. Since, however, it can be safely affirmed of no 
aneroid, how good soever it may have proved itself to 
have been, that it will continue to indicate correctly for 
even a brief time to come, the Conference came to the 
sound conclusion that the aneroid should not be used 
instead of the mercurial barometer, but only as an inter- 
polation instrument, to fill up blank when the mercurial 
barometer is out of order, or when it cannot be observed 
on board ships in rough weather. 
Maximum and Minimum Thermometers.—Ruther- 
ford’s minimum spirit thermometer was regarded as 
satisfactory. On it being pointed out by several mem- 
bers that this thermometer is liable to go out of order by 
the spirit evaporating and condensing in the upper end of 
the tube, Ebermeyer, of Aschaffenburg, stated that this 
objection could be removed if the tube were at its en- 
trance into the bulb inserted nearly up to the inner side 
of the bulb. We commend this suggestion to opticians ; 
for if Ebermeyer’s experience be confirmed, a source of 
serious and not infrequent error will be remoyed. On 
the other hand the performance of no maximum thermo- 
meter was considered to be so satisfactory that a uniform 
construction could be generally recommended ; and the 
opinion was expressed that it was very desirable that a 
trustworthy maximum thermometer was devised, not 
liable for instance to have the mercury disturbed during 
high winds like Negretti and Zambra’s, or the index por- 
tion go out of order as Rutherford’s or Phillip’s, 
Instruments for Radiation—Mr, Symons, who has 
paid much attention to this question, has been requested 
to give a report to next Congress on the modes of obser- 
vation adopted in England for radiation. But it must 
be confessed that the methods of observation in this im- 
portant inquiry are still in a very primitive state. Mr. 
Salt well pointed out that at present the results obtained 
with different instruments were not comparable with each 
other, and one hardly knew with the instruments now in 
use what was really observed. 
Aygrometers—Since the dry and wet bulb hygro- 
meter is not trustworthy at low temperatures and in cases 
of extreme dryness, and the hair hygrometer fails also at 
the dew points, and since there is no hygrometer yet de- 
vised, at least for regular observations at stations, which 
gives approximately exact results as to moisture in all 
cases, it was recommended to make further experiments 
and collect the experience of meteorologists on the sub- 
ject. From the favourable opinions expressed by Wild 
and others of the action of the hair hygrometer, further 
experiments with this instrument are very desirable, so 
that it might be made available for more accurate ob- 
servations on the hygrometry of the air at temperatures 
below the freezing-point than the dry-and-wet hygrometer 
admits of. Another desideratum is an extensive series of 
experiments with Regnault’s hygrometer in conjunction 
with the dry-and-wet bulb hygrometer in dry hot climates 
such as N.W. India, for the purpose of ascertaining how 
far the readings of the dry-and-wet bulbs can be used as 
data from which the dew-point may become known ; and 
~ determining the requisite data for the correction and com- 
pletion of the present hygrometric tables, particularly at 
points below freezing, and at high temperatures combined 
with great dryness. 
Wind.—Curiously enough, the question of proper in- 
struments for measuring the velocity and force of the 
winds does not seem to have been under discussion, even 
though it is one of the most important and pressing ques- 
tions of the science. Anemometers, both for velocity and 
pressure, are indispensable to properly equipped observa- 
tories, Now it cannot yet be said that the anemometers 
for velocity give quite correct indications that they are 
comparable, ztex se, and that we have a practicable 
means of ascertaining their errors from time to time. 
Equally remarkable was the omission in the discus- 
sions, to consider what are the required conditions which 
anemometrical stations ought to fulfil, so that the instru- 
ment shall indicate the true movement of the air over 
the region where it is placed ; or, if this cannot be ac- 
complished, what observations should be instituted in 
order to ascertain how far the direction of the wind is 
deflected by the physical configuration of the surface, 
and its force diminished (or in rare cases accelerated) as 
compared with the general movement of the air over the 
place. 
Pressure anemometers at a moderate cost are a great 
desideratum. Little satisfactory is known of the relation 
of pressure to velocity. 
Rain.—The Committee proposed that a report of all 
the experience regarding the position, size, height aboye 
ground, and time of reading the rain gauge which has 
been yet gained should be prepared for the Vienna Con- 
gress. For the preparation of such a report the great 
storehouse of facts at hand are those collected by Mr. 
Symons in the successive parts of his “ British Rainfall” 
and “ Meteorological Magazine,” which the members of 
the Congress would do well to consult. 
Evapometer.—The present state of the evapometer is 
one of the least satisfactory of all the meteorological 
instruments. Considering the importance of the drying 
property of the air in relation to meteorology generally, 
but especially as one of the most important constituents 
of climate, it is to be hoped that some method will be 
devised by which results, at least roughly a a to 
begin with, may be obtained. 
The difficult, but vital question of the position of the 
thermometer does not seem to have been faced by the 
conference, Itis earnestly hoped that the Vienna Con- 
gress will not shirk this question, but will seriously dis- 
cuss it and arrive at some decision, or suggest some steps 
to be taken, that will ultimately lead to the degree of 
uniformity which is so imperatively called for. Till this 
be secured, the expensive systems of horary or contin- 
uous registration of temperature carried on at the great 
observatories of this and other countries, cannot supply the 
data for the determination of temperature “constants,” see- 
ing that they are incomparable with each other, as well as 
with the observations made at those numerous stations of 
the secondary order to which we must look for the work- 
ing out of the great national question of local climates in 
their bearing on the health, productions, and commerce 
of the country. The question would be of comparatively 
easy solution were it possible, in the interests of cosmical 
inquiries, to ignore the past, But it is essential in the 
