The sun. [volume] (New York [N.Y.]) 1833-1916, 1900-05-06

or even longer may be found advantageous,
but exposures from ? seconds up 10 so OF
~ or upward, require the most skilful manipu-
lhtion in development 10 render them Of any
service otherwise detail in the corona proper
ia sacrificed withou, any sensible increase
in the representation Of The streamers, Triple
coated tnOn-halatiOn) plates should be used for
such long exposures, and the ~ondition Of the
| sky will have to be- taken into consideration.
II the atmospheric glare IN tue. vicinity 81 the
sun be- great, or II Il diminish more slowly
than the corona a. The distance from the sun
increases, a limit will be reached beyond which
the treamers cannot be photographed,
The one and only caution TO be borne in
mind Is that the camera should be firmly and
rigidlv mounted
The choice Of Instruments is no, limited TO
cameras and Photographic telescopes. Prof
Bnrnard's beautiful photograph Of the corona
of the 1854 California eclipse shows that A
visual objective, with the aperture sufficiently
reduced. may give excellent results lie used
a 3'2-lnCh Clark equatorial, ~ inches focal
length, with the aperture reduced 10 u, inches.
With an exposure of A. seconds on "A moder-
tent Of the corona and as great wealth of detail
as Prot. Pickering with his l3-inch Photographic
telescope Of 1876 inches focal length, the latter
using a slow plate.
In focusing the instrument. il should be
pointed at 4 well-defned object, distant, say,
from a quarter mile to II mile, aud the object
brought TO a sharp focus fer The centre of the
q small object. and occupies but n COMPARE
lively small part of the centre OF tho field
Inc local length of the camera In inches will give
roughly. the diameter OF the suns image in
hrndredths OF an inch. The image of the
corona will be from two TO -four times these
dimensions.
80 secure the best results. however, II would
be better 10 determine the stellar focus by
photographing trails ~ stars, and selecting
me adjustment which gives the sharpest dcf-
nltlon fineet llne) IN the centre Of the field.
In this connection, II * important TO notice
that Prof. Barnard's success with the visual
,elesoope' noted above, was made possible by
fhe Photographic focus " his instrument.
one preGautton must be rlSidly observed
the original negative, must not be retouched
or altered, as II VIII destroy entirely its sCien-
tiiC value.
The United States Naval Observatory will
publish an extensive report on tho eclipse
results, and would he glad to include photo
graphs which may possess sufficient scientific
merit. II the original negative is sent to the
OBSERVATORY. II viii he returned after using.
Inc data accompanying such negatives Should
include a description of the apparatus. kind
Of plate and developer. length Of exposure
and location of station. The plate should
also have been marked previous To- exposure
To indicate the top side OF the plate,
TELESCOPE OBSERVATIONS.
Telescopes A proper telescope for obsery-
Ing the eclipse is very desirable. but any telescope
AT all is better than none. and ow uers OF small
spyglasses. or opera-Rl0sses, should benr in
mind that their instruments are capable of
doing good service. Opera-glasses can be
held in the hand with sufficient steadine,s,
but spyglaSses, however small. will reuuirr n
stand to produce the best effect This need moi
be an elaborate affair, but may 10 made of wood
IN ne simplest manner provided only that IL Is
in any required direction. Some artificial sun
port Is necessary and, in default Of any thing
better, the telescope might even be dashed
10 n round post.
Shade glasses For the first and last contact
shade glasseswill he necessary. The most usual
color for n shade is rcd, Either "A neutral TIM
or green is excellent,
TUE foIR CONTACTS.
As the moon by, her motion overtakes the
sun. the eclipse always begins on The west
side OF the solar disk isee Fig. u. First contact
takes place when the advancing moon first
touches the west Edge oi the sun. second con-
tact Is the beginning. third, the ending OF to-
taity. Fourth contact IL the very end OF the
eclipse. The times Of all four contacts should be
noted.
n party to observe the contacts should
consist OF TWO persons, one OF whom should
have a tmepleCe and writing materials and
the other a telescope. With regard To the latter
instrument, II may be remarked that if It is
n common one "A spyglass, tor instance
there VIII probably he no choice ~ To It's mag
nl!ylng power, hut il II belongs 10 The better
class, and has n battery of eyepleces, the power
chosen should bc equal to fifteen or twenty
times the diameter ot the objective in inches.
To secure the best results the party should b,
entirely alone, above nil. not within hearing
or other observing parties. 4 minute or 80
before the expected time ut contact the person
with the timepiece will fix his eyes unon lis
second hand and begin silently TO CONN., tb.
seconds, while the observer the telesCnpa
will carefully watch the sun. Upon the oc-
rurrence OF contact the observer ~ viii cry
Marx, and the person NJ the timepiece will
immediately write down, first. the second
then, the minute, and, finally, the hour. Be-
fore beginning To observe care must be taken
10 soc that when the second hand points 10 90
The minute hand i exactly over n minute mark
and, In observing, II the seconds are near
sixty, special care will he required to avoid
recording n wrong minute, Practice in call
lng and noting nmc previous TO the eclipse
will greatly diminish the risk of such mistakes.
A little before totality n lantern should
be lighted. because without il there may 5e
difficulty in seeing the hands of the timepiecr
al the approach oI third contact,
Thermometer or tlmepiece, Observations
OF the internal contacts can be utilized without
q knowledge ot the error % the ttmepiece.
but with the external contacts the ease is AT
icren'. They will he Of no value url.ss the
error Of the tlmepiece j. accurately known.
either on local or on " ashington limp. To
meet this difficulty. II j. hoped that arrange
lnents may be made 10y which the Westerr
al cost, a signal from the Naval Observatory,
indicating n" instant Of Washington mean noon,
10 al proper persons who, may apply for 1t
al any OF their office, on May 20. Is and ~
Tho lntcndln g observer can hest utilize these
signals by making SIRE that the minute and
second hands OF his watch agr"e with each other.
az explained above. and then carrying the watch
10 the telegraph otfiC, ou each of the days men
toned and noting the hour. minute and second
indicated ON II when the signal j. received.
NJ matter how the watch may run. IL must not
h' meddlad with IN any way. either by moving
lis hands or touching its regulator. between
May 20 and Nav 20. Without This prccaution.
neither it, rate. nor the degree OF dependence,
To be placed upon II, can be- determined.
The final record Of a set of observations
Of contacts should contain the following in
Formation
First The naWe ~ TIVE -tatiOn: including
town, county and state
80 'oud The date
Third \ description 81 the ~locatiou Of tho
station with reference In The nearest prominent
l~animark-. a., for example. it, bearing and
distance from the nearest court house. rail
road station OF church VI It's position with