The Republican. [volume] (Oakland, Md.) 1877-current, 1886-01-02
MEASURING SUNSHINE.
How the English Scientists Have Solved
Great Problem.

a Great Problem.
When the British Association first
met at Birmingham, in 1889, the famous
French astronomer, Arago, was pres
ent. The weather was cloudy, and
when at the end of the meeting it
cleared he formally took off his hat to
the sun, as he declared he had begun
to fear that he had come to land
where that luminary would never show
his face again This was, of course,
only joke of Arago's, but in the
course Of this last spring two Russian
officers were visiting Kew Observatory,
and on being shown the apparatus for
sunshine registration and for solar
photography, these gentlemen eX-
pressed their honest surprise that such
researches should be attempted, as it
was a well known fact TINT the sun
never shone in England.
1t is, however, in that country that
the subject of sunshine registration has
received the most attention and been
the most successfully studied. 1t is
now nearly half century ago that
plan for recording sunlight photograph
ically and continuously throughout the
day was submitted to the Royal Corn
wall Polytechnic Society by Mr. =.
Jordan, while the proposal of the late
Mr.. j. f. Campbell, of Islay, for reg
Iistering the sun heat dates from the
| year 1858, and was described in the re-
lport ofthe British Meteorological So
! ciety for 1857. 1t is this latter process
(which has met with general acceptance,
as it entails so little trouble. The record
consists in the amount of charring an
organic substance such as wood or
paper undergoes from the solar action,
and which is of course perceptible to
the eye. The Photographic process, on
the other hand, always entails certain
amount of development of chemical
treatment, even though of simple
nature, to render the solar trace visible.
The least reflection will show the
reader that in order to obtain contin-
uous record of sunshine throughout a
| cloudless day, some contrivance is nee
| essary to follow, so to speak, the sun in
his course. This was formerly done
by means of an instrument termed a
whatever be his altitude, were always
| reflected along the same direction
throughout the day. This entailed the
employment of clockwork to drive the
rejecting mirror, and a similar power
was also required to move the paper
past the slit through which the SUMS
rays were admitted.
Mr.. Campbell hit on the very ingen-
ious notion of employing glass sphere
as lens, so that as the sun travelled
round the ball its image should travel
round on the opposite side. The first
instrument consisted of ball placed in
side mahogany bowl, turned to the
exact focal length of the ball. Such a
bowl was capable of receiving record
for six months from one solstice to the
next. 1t was, however, impossible to
distinguish the record of consecutive
| days from each other, and accordingly
a plan had to be devised by which the
record could be obtained on a slip OF
card board or other material which
could be replaced daily.
| A very ingenious frame was finally
devised by Prof. Stokes, of Cambridge,
provided with grooves into which the
cards are slipped. The grooves are in
three pairs-for the summer, the win
ter and the equinoXes respectively and
the cards have hour lines printed on
them. The instrument can thus be
used as a sun dial, for the spot where
the solar image appears-where the
burning is taking place-of course cor.
responds to the spot where the shadow
of the gnomon would cut the scale Of
the dial. These instruments were first
brought out at the end of 1879, and by
this time there are nearly fifty of them
in various parts of the United Kingdom.
| The MicrOcOSm.