SCIENTIFIC SUMMARY. 
519 
recommended that we should profit, and that at once, by the electric cable 
which connects the New and Old World, in order, to determine the exact 
longitude of the American station. 
A new Spectroscope has been constructed by Father Secchi, and seems to be 
a very excellent instrument. It absorbs a very small quantity of light, and 
is therefore admirably adapted for stellar observations. The inventor has 
analyzed with it the spectrum of the light emitted by the star Antares. It is 
of a red colour, the luminous bands have been resolved into bright lines, and 
the dark ones are chequered with light and dark lines, so there is no black 
foundation. — The Reader, August 25th. 
A New Magnesium Lamp. — An ingenious form of magnesium lamp, the 
invention of Mr. H. Larkin, and which was first exhibited at the Eoyal 
Institution a couple of months since, was shown at the soirees of the British 
Association at Nottingham. Instead of the ordinary ribbon or wire of the 
commoner forms of magnesium lamps, magnesium powder is employed. 
Hence all machinery is dispensed with, the magnesium being contained in 
a reservoir, from a hole in the bottom of which it falls like sand from an 
hour-glass. The powder is allowed to fall upon the flame of a small gas 
jet, and by this it is inflamed, giving all its usual illumination. In order 
that a sufficient quantity of powder may be employed, and that the hole in 
the reservoir may be large enough to allow of a regular flow, without waste 
of magnesium, the latter is mixed with fine sand. The size of the aperture 
is regulated by a stop-cock. When it is desired to light the lamp, the gas is 
first turned on, just sufficiently to produce a small jet at the mouth of the 
tube, which small jet, being once kindled, may be allowed to burn any con- 
venient time, until the moment the magnesium light is required. All that 
is then needed is to turn on the metallic powder, which instantly descends 
and becomes ignited as it passes through the burning gas. This action of 
turning on and off the metallic powder may be repeated without putting out 
the gas, as often and as quickly as desired ; so that, in addition to the ordi- 
nary purpose to which lamps are applied, an instant or an intermittent 
light of great brilliancy, suitable for signals or for light-houses, may 
be very simply produced with certainty of effect and without the smallest 
waste of metal. The first evening an objection was made that the blue 
tone of the light created a cold and somewhat ghastly effect. On the 
second occasion Mr. Larkin remedied this by mixing with the magnesium a 
certain quantity of nitrate of strontia. — Vide Journal of the Society of Arts, 
September. 
What is the Cycloscope ? — It is an instrument for setting out railway or 
other curves without the aid of a theodolite, and has been devised by Mr. 
H. Temple Humphreys, Assoc. Instit. C.E. It is composed of two essential 
parts, viz., two plane mirrors, one entirely silvered and the other silvered on 
only one-half of its surface. In accordance with the “ law of successive or 
combined reflections,” a series of images are formed in the half-mirror which 
may be rendered available to set out any curve, of any given radius, by 
applying the eye to an aperture in the entire mirror, and at the same time 
setting the two mirrors at an angle equal to the required tangential angle. 
By this operation the several successive images of a ranging rod are seen to 
lie on the circumference of a mathematically true circle. “ The curve was 
