o20 Chronicles of Science. [April, 



tions which it has suffered, the dispersion, at its exit, is added to the 

 dispersion at its entrance instead of being subtracted from it, as 

 would have been the case had only one reflection taken place. The 

 instruments are made with two such prisms connected together by 

 their like ends ; the combination producing a direct vision spectro- 

 scope, of which the dispersive power is four times greater than that of 

 any single surface of the prisms. "With a magnifying power of 5 

 only, Fraiinhofer's line D is appreciably separated, whilst the other 

 dark lines are seen with much distinctness and in great numbers. 

 The slit is fixed on a slider, by means of which arrangement any part 

 of the spectrum may be brought into the field of view. 



It is to be hoped that some information will soon be obtained 

 respecting the composition of meteors from the colours which they 

 assume. Data for such theoretical discussions are being gradually 

 accumulated. Mr. Schmidt has recently communicated to the Belgian 

 Academy some observations made at Athens on the colours of shoot- 

 ing stars ; he finds that red and green coloured meteors are most often 

 seen in summer. The author has noted the colour of 5,671 meteors ; 

 4,300 of these were white, 905 yellow, 320 red, and 146 green. 



With one useful application of light to the requirements of every- 

 day life we will conclude our chronicles of this branch of science. In 

 some parts of Paris some very successful attempts have been made to 

 render the names of the streets as visible at night as in the day time. 

 In the neighbourhood of the Hotel de Ville, the names are now lighted 

 up in the following manner : — the frame in which the letters are set is 

 made in the form of a rectangular trough, the upper and lower portions 

 being pierced with holes to allow of proper ventilation, and within this 

 is a gas pipe with a number of small jets, according to the length of 

 the tablet ; in front of these jets are arranged the transparent letters 

 which are thus brightly illuminated. The upper part of the box or 

 trough opens to allow of lighting and repairs, and is closed by a 

 counterpoise concealed in the stone work of the walls. 



Heat. — Professor Tyndall has communicated to the Royal Society 

 the results of his important researches on the invisible heat radiation 

 of the electric light. The distribution of heat in the spectrum of the 

 electric light was examined by means of a linear thermo-electric pile. 

 The electric spectrum was formed by lenses and prisms of pure rock- 

 salt, its width being equal to the length of the row of elements form- 

 ing the pile. The latter standing at right angles to the length of the 

 spectrum was caused to pass through its various colours in succession, 

 and to search the spaces beyond the region of colour in both direc- 

 tions. As in the case of the solar spectrum the heat was found to 

 augment from the violet to the red, while the maximum heating effect 

 was observed beyond the red. The augmentation of temperature be- 

 yond the red in the case of the electric light is sudden and enormous, 

 being much greater than that obtained by Professor Midler for the 

 solar spectrum. Aqueous vapour acts powerfully upon the invisible 

 rays, and doubtless the action of this substance in our atmosphere has 

 modified the intensity of the rays beyond the red. In the experiments 



