April 26, 1873.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
847 
portion is seven or eight times as great as from the 
luminous or visible. 
The effects of the invisible rays in nature may now be 
instanced. The action of the sun on the tropical ocean 
results in warming the waters and vaporizing a portion 
for the production of rain and snow. It is the dark rays 
which accomplish these results. The light rays go deeper 
down. The non-luminous rays go but a short distance 
below the surface. Rivers are liberated by these same 
invisible rays. To enable you to see more clearly that it is 
the dark and not the light rays which produce these effects, 
I reflect the beam from the electric lamp by a mirror, and 
mark by a stick the place of the luminous focus. Now, 
placing the thermo-electric pile in this focus, you see the 
image of the needle deflected on the screen. Let us now 
cut off the light. Placing the pile where the focus of light 
was, the needle is still deflected though no light is at 
the focus. 
By means, of the Nicol’s prisms we may polarize heat 
as well as light. They are introduced, and, when rotated 
to the proper angle with each other, polarization occurs. 
This polarized heat may be transferred to the thermo¬ 
electric pile, and its existence and amount shown by the 
deflection of the galvanometer needle. 
The same effects may be produced with radiant heat 
as with light. Radiant heat is like light, capable of re¬ 
flection, refraction, polarization both plain and circular, 
and double refraction. I will now cut off the light, and 
when I introduce a sheet of mica, the needle which 
previously was at zero will be deflected 90°. 
{To be continued.) 
RECENT PROGRESS IN WEATHER KNOWLEDGE.* 
BY ROBERT H. SCOTT, F.R.S., 
Director of the Meteorological Office. 
The prediction of the seasons, for any considerable 
period in advance, is of course a problem whose solution 
must affect the most important social interests, inasmuch 
as all the operations of agriculture are necessarily depend¬ 
ent on the varying character of the weather. Recently, 
in order to afford some practical information as to the 
effect of the weather on growing crops, an agitation has 
been set on foot for the organization of a system of tele¬ 
graphic agricultural weather reports, in order, by a know¬ 
ledge of the prospects of the harvest, to be able to regulate 
the price of grain. The late Commander Maury took an 
active part in this movement, and the question was mooted 
at the International Statistical Congress at St. Petersburg 
last summer. 
Meanwhile, in the course of last summer, a commence¬ 
ment was made in England of giving intelligence as to 
the probable growth of crops, by adding six inland 
stations to the list of those which furnish information for 
the daily weather report. 
Our recent experience of the rainfall of 1872, which 
was almost unprecedented and certainly unexpected, both 
as to its amount and continuance, is a fair illustration of 
the very moderate pretensions which even the most prac¬ 
tised meteorologists can make to a knowledge of the 
probable character of the weather for even two months 
in advance. Abundant notes are now being received as 
to the concomitant phenomena of unusual drought during 
parts of last year in other regions of the earth, and as to 
the abnormal relations of barometrical pressure over north¬ 
east Europe on the one hand and Iceland on the other ; 
but none of these facts throw any light, hitherto discover¬ 
able, on the causes of our exceptional weather. 
Numerous instances might be cited of the failure of 
prophecies of weather based on the popularly-received 
signs, such as the shining of the sun on Candlemas Day, 
* Abstract of a Lecture delivered at the Royal Institu¬ 
tion of Great Britain, Friday, February 14th, 18/3. 
evidencing that the principles on which such prophecies 
depend are not mathematically correct. It is, neverthe¬ 
less, undeniable that the movements of birds of passage 
are apparently directed by a prescience of the coming 
character of the weather; generally, their arrival may be 
attributed to the fact that they herald the approach of con¬ 
ditions of weather which have already set in in their home. 
Changes of weather ought to bear mathematical treat¬ 
ment as well as any other statistical facts, and conse¬ 
quently attempts have been made to apply mathematical 
reasoning to experience of the seasons, in order to test 
whether these popular ideas have or have not, any real 
basis of truth. 
The most recent contribution to knowledge in this 
direction is a paper by Wladimir Koppen in the Russian 
Repertorium fur Meteorologie, vol. ii., “ On the Sequence 
of the Non-periodic Variations of Weather, investigated 
according to the Laws of Probability.” The discussion is 
prefaced by the remark that while weather study has 
made great progress owing to the development of tele¬ 
graphy, its results are mainly of utility to the seaman, 
but remain comparatively valueless for the farmer, while 
the advantage to be derived from a foreknowledge of 
the weather is as great in the one case as in the other. 
Koppen has examined into the chance of a change of 
weather at any time, and he finds that the wecdher has a 
decided tendency to preserve its character. Thus, at 
Brussels, if it has rained for nine or ten days successively, 
the next day will be wet also in four cases out of five; 
and the chance of a change decreases with the length of 
time for which the weather from which the change is to 
take place has lasted. 
In the case of temperature for five-day periods the same 
principle is found to be true; for if a cold five-day period 
sets in after warm weather, the probabilities are two to one 
that the next such period will be cold too; but if the cold 
has lasted for two months, they are nearly eight to one 
that the first five days of the next month will be cold too. 
The chance of change is, however, greater for the five-day 
periods than for single days. Similar results follow for 
the months, but here, again, the chance of change shows 
an increase. 
In the instance we first cited, that of rain, the result 
is not that if it once begins to rain the. chances are in 
favour of its never ceasing; all that is implied is, that 
the chances are against its ceasing on a definite day, and 
that they increase with the length of time the rain has 
lasted. The problem is similar to that of human life : 
the chance of a baby one year old living another year is 
less than that of a man of thirty. 
The practical conclusion from all this is, that although 
it is known that a compensating anomaly for all extraor¬ 
dinary weather exists somewhere on the earth’s surface,— 
e. g. the very common case of intense cold in America 
while in this country we have a mild winter, which was 
most strikingly true last January,—there is no reason, as 
yet ascertained, to anticipate that this compensation will 
occur at any given place in the course of a year. In 
other words, when definite conditions of weather have 
thoroughly established themselves, it is only with great 
difficulty that the courses of the atmospheric currents are 
changed. 
Attempts have not unfrequently been made to predict 
the seasons for a long period in advance, but without much 
success hitherto. One great cause for failure is, that accu¬ 
rate meteorological records do not extend beyond the 
beginning of the century at more than a few stations, and 
for these the local influences cannot be altogether elimi¬ 
nated. Thus, it is hardly possible to say what has been 
the approximate temperature of these islands for more 
than twenty years,—a period far too short for the definite 
recognition of a cycle. The shortest of these cosmical 
cycles which has been determined is the sunspot period of 
11} years according to Wolf, and there are indications of 
far longer periods, such as 33 years or even 09-} years, 
according to Hornstein. 
