SUGGESTIONS TO ASTRONOMERS. . 363 
shadow’s movement. Thus Arendal, Friederichsvarn, Christiania ; 
Kulm, Danzig, Konigsberg; Warsaw, Ostrolenka or Lomja, Au- 
gustowo; Brody, Brest-Litowsk, Grodno ; Nikolaiew, Babrinez, Je- 
lisawetgrad ; &c., would be favourable combinations. Two or three 
such confederations should be formed at different parts of the 
shadow’s path. 
5. It is desirable that, at each station, there should be three or 
four observers. One should be furnished with a telescope magni- 
fying about twenty times, with a pretty large aperture ; and this 
will probably be found the most important. A second should have 
a telescope magnifying 100 times. Hach of these telescopes should 
have in its field, but not crossing the centre, two wires of an inter- 
val of 1’, or some other convenient distance, for giving an approxi- 
nate measure of any small object which may be observed. It is de- 
arable that by the position of these wires, or in some other way, 
he observer should be able rapidly to refer the positions of objects 
een in the telescope to vertical and horizontal directions. A third 
person should have a watch or chronometer (if the error of the 
chronometer is known, the astronomical value of the observations 
will be increased, but their physical value will be equally great 
without it) and writing materials, and should be prepared at any 
signal first to note the time, and secondly, to write down the phe- 
nomenon. A fourth should observe the general appearances, as seen 
with the naked eye. If the party were more numerous, a good 
sextant, or other double-image instrument, might be found useful 
in the hands of one person. 
6. It is important that the dark glasses used for observing the 
sun up to the moment of total obscuration be so mounted that they 
ean be slipped off in an instant. And it is desirable that each tele- 
scope should be furnished with several dark glasses, some showing 
the sun with a red disc, some with a white or greenish disc. These 
may be mounted, in a form which admits of rapid change, in a 
slidmg or a turning frame ; or their cells may be fitted loosely with 
bayonet-notch. If the observer is satisfied with the use of one co- 
lour or combination for the dark glasses, no arrangement is more 
convenient than that of wedges of the coloured glass, achromatized 
(as to dispersion) by wedges of colourless glass; the intensity is 
then changed gradually by merely sliding the combination of 
glasses. It may also be desirable to possess the power of altering 
the aperture of the telescope rapidly: this perhaps may be done by 
attaching by hinges to the object-glass cell one or more flat rings, 
which can be turned off or on the object-glass by pulling a string 
at the eye end. 
7. It is desirable also that the observers should be provided with 
some instrument for the measure of radiant heat, as a thermomul- 
tiplier (of a coarse kind) with galvanometer, an actinometer, or a 
simple thermometer with rough black bulb (whose indications will 
be more accurate if the bulb be inclosed in a glass sphere from 
