SCIENTIFIC SUMMARY. 261 
mine their places, with reference to the bodies in which their number or 
position would be found remarkable. — Yide Comptes Rendus, January 2. 
A New Method of Registering the Results of Spectrum-analysis is being 
successfully employed at the Kew Observatory. By its means the exact 
distances of the lines from each other and their relative positions are 
accurately delineated. Briefly the process is as follows : — The paper on 
which the lines of the spectrum are to be drawn is rolled round a cylinder 
whose circle is graduated and is provided with a vernier. By means of an 
apparatus for the purpose, the cylinder may be turned with exactitude to 
any required extent, and when it is stopped, a line may be readily traced 
upon the paper by means of a rule. The angular distances between the 
spectral lines are given by the graduated circle of the instrument. 
A Substitute for Magnesium Light has been suggested by M. Sayers, and 
promises to be of much service in physical operations in which photography 
is employed. Twenty-four parts by weight of nitrate of potash, seven parts 
of flowers of sulphur, and six parts of red sulphide of arsenic, are thoroughly 
mixed. This composition, when set on fire, affords a most brilliant light, 
and the negatives produced with it give excellent positives. It has been 
found that about half a pound of the mixture will afford light for half a 
minute. 
Ladd's Modification of Marcus' Thermo-electric Battery. — This instrument 
was exhibited at the Soiree of the Koyal Society on the 10th of March. The 
principle is the same as that of other batteries of this class. A series of 
thermo-electric elements, consisting of bars of German silver (nickel, copper, 
and zinc) soldered to other bars compounded of an alloy of antimony, zinc, 
and bismuth (only one part in 18 of the latter), are heated at one end by a 
series of what are really small Bunsenburner jets, when electrical action 
is set up in the usual well-known manner. To a large induction-coil, and to 
a soft iron core the wires of the thermo-electric battery were alternately 
connected to show its power. — Yide The Reader , March 17. 
Artificial Cobwebs for Telescopes. — The telescopes used in engineering 
operations are provided with cross-wires of delicate spider’s-web ; but, as 
these frequently become broken, and cannot be easily replaced in a short 
space of time, the following substitute has been suggested in the Archiv fur 
Seewesen. The threads to be substituted are made of glass, and may rapidly 
be prepared in a case of emergency. The process is as follows : — Take a 
thin slip of window glass, and heat it at the centre in the flame of a lamp. 
When the glass is red hot, the strip may be pulled apart, and two pieces with 
pointed ends are formed. Each of these is to be heated in the flame until a 
small button has formed on the end, and whilst they are still hot the two 
buttons are to be brought into contact with each other. If the two be now 
pulled quickly apart, a thread will be produced, the fineness of which will 
vary according to the softness of the glass and the rapidity with which the 
hands are separated. A very little practice will be sufficient to enable any 
one to manufacture a thread of sufficient fineness for use in a telescope when 
it would be impossible to procure a piece of spider’s-web. 
