Sculptured Emaciated Figures (Vol. v., p 497.; Vol. vi. passim).—In Dickinson's Antiquities of Nottinghamshire, vol. i. p. 171., is a notice with an engraving of a tomb in Holme Church, near Southwell, bearing a sculptured emaciated figure of a youth evidently in the last stage of consumption, round which is this inscription: "Miseremini mei, miseremini mei, saltem vos amici mei, quia manus Domini tetigit me."
J. P., Jun.
Do the Sun's Rays put out the Fire (Vol. vii., p. 285.).—It is known that solar light contains three distinct kinds of rays, which, when decomposed by a prism, form as many spectra, varying in properties as well as in position, viz. luminous, heating or calorific, and chemical or actinic rays.
The greater part of the rays of heat are even less refrangible than the least refrangible rays of light, while the chemical rays are more refrangible than either. The latter are so called from their power of inducing many chemical changes, such as the decomposition of water by chlorine, and the reactions upon which photographic processes depend.
The relative quantities of these several kinds of rays in sun-light varies with the time of day, the season, and the latitude of any spot. In general, where the luminous and heating rays are most abundant, the proportion of chemical rays is least; and, in fact, the two seem antagonistic to each other. Thus, near the equator, the luminous and calorific rays being most powerful, the chemical are feeble, as is shown by the length of time required for the production of photographic pictures. Hence, also, June and July are the worst months for the practice of photography, and better results are obtained before noon than after.
It is precisely for a similar reason that the combustion of an ordinary fire, being strictly a chemical change, is retarded whenever the sun's heating and luminous rays are most powerful, as during bright
sunshine, and that observe our fires to burn more briskly in summer than winter; in fact, that apparently "the sun's rays put out the fire."
A. W. W.
Univ. Coll., London.
Spontaneous Combustion (Vol. vii., p. 286.).—A most interesting discussion of this question is to be found in Liebig's Familiar Letters upon Chemistry.