SCIENTIFIC SUMMARY. 
293 
in it. A stoppered bottle, made to hold a pint of water, weighs when 
empty but four ounces, a mere fraction when compared with its weight 
when filled. The shallow dishes or trays, developing cups, funnels, and 
other smaller requisites, may likewise be procured of this material, all of 
which are proportionately light and compact. 
A very perfect description of prepared silk for covering the windows of 
the dark room has recently been introduced by Mr. Smartt. It consists 
apparently of two layers of oiled silk, with a deep orange, almost scarlet, 
pigment laid between ; it is uniform in colour, and very durable. The 
material is made in pieces measuring three feet by eighteen inches, and a 
single thickness is sufficient to cut off all the chemically active rays of 
sunlight. 
It is well known in London, that for five shillings may be purchased very 
beautiful reduced photographic copies of Rosa Bonheur’s “ Horse Fair,” and 
Holman Hunt’s “Light of the World the original engravings, by Mr. 
Thomas Landseer and Mr. Simmonds respectively, costing as much as 
ten guineas. The copyright of these works of art being held by Mr. 
Gambert, of Pall Mall, that gentleman has thought proper to take law 
proceedings, in order to protect himself against the piratical imitation, by 
means of photography, of these and other engravings published by him. 
The question of copyright has therefore been repeatedly discussed in 
the course of the arguments advanced by the plaintiff and defendants in 
these actions. It cannot, however, be said to be well defined, when it has 
been found necessary to refer back to Acts of George III., so long before 
the invention of photography, and when the words “fac-simile” and “main 
design ” were intended to apply to copies or reproductions of the same size 
and style, and to such works as would be likely to deceive the purchaser 
at the time of making his bargain. It is clear, then, that a special Act 
must be obtained of more general application in these cases, and that the 
copyright of an engraving must forbid alike the reproductions of photo- 
graphy, as well as all other attempts by older processes of imitative art. 
EVERAL papers have been published since our last number, somewhat 
modifying our views of the supposed rigidly definite character of 
spectrum analysis. M. Pliicker, in a letter in the “ Cosmos,” shows : — 1st. 
That the spectra of gases and vapours vary with the power of the induction 
coil, and show a tendency to continuity by spreading of the rays. 2nd. That 
this variability and spreading are caused by rise of temperature, so that 
the number and kind of the rays are dependent upon the temperature to 
which the gases are subjected in the capillary tubes. And 3rd. That by 
simultaneously increasing the density and temperature of highly rarified 
gases, there may be made to appear and disappear the various rays which 
constitute their spectra — alternated, separated, and reunited by the power 
PHYSICS. 
LIGHT, HEAT, AND ELECTRICITY, 
