THE general view held by philosophers seems to be that when temperature rises the gravitative attraction changes (if at all) by a function of temperature only. This leads to the results stated in the beginning of their letter by Dr. Lindemann and Mr. Burton. But it is commonly conceded that at present there is no trustworthy theory of gravitation, so that one seems entitled to suggest that any increment in the force may be a Junction of both mass and temperature. The simplest formula, that of the weighted mean temperature, brings the facts as at present known into line. It seems that we must await further data; for, of course, a fact, however slight, may shatter a theory lying in its course.