216 Mr. F. W. Barrett on Sensitive Flames. 



ture of the earth's surface would therefore necessarily begin to 

 rise, and would continue to do so till the rate of radiation from 

 the surface would equal the rate of radiation received by the 

 surface. Equilibrium being thus restored, the temperature 

 would remain stationary. It is perfectly obvious that if we 

 envelope the earth with a substance such as our atmosphere, 

 that offers more resistance to terrestrial radiation than to solar, 

 the temperature of the earth's surface must necessarily rise until 

 the heat which is being radiated off equals that which is being 

 received from the sun. Remove the air and thus get quit of the 

 resistance, and the temperature of the surface would fall, because 

 in this case a lower temperature would maintain equilibrium. 



It follows, therefore, that the moon, which has no atmosphere, 

 must be much colder than our earth, even on the side exposed to 

 the sun. Were our earth with its atmosphere as it exists at 

 present removed to the orbit of Venus or Mars, for example, it 

 certainly would not be habitable, owing to the great change of 

 temperature that would result. But a change in the physical 

 constitution of the atmospheric envelope is really all that would 

 be necessary to retain the earth's surface at its present tempera- 

 ture in either position, as has been clearly shown by Professor 

 Tyndall*. 



Erratum in No. 221. 

 Page 130, line 18 from top,/or thousand read hundred. 



XXIX. Note on "Sensitive Flames." By W. F. Barrett, Teacher 

 of Experimental Science at the London College of the Interna- 

 tional Education Society, late Assistant in the Physical Labo- 

 ratory of the Royal Institution-^. 



IN the last Number of the Philosophical Magazine Professor 

 Tyndall has published the abstract of his Friday evening 

 lecture at the Royal Institution, " On Sounding and Sensitive 

 Flames." In the historical note prefixed to that abstract, Pro- 

 fessor Tyndall has stated my relationship to the latter subject. It 

 is briefly this. In 1865, while preparing the experiments for one 

 of the Christmas lectures at the Royal Institution, I noticed that 

 the higher harmonics of a brass plate (which I was sounding with 

 a violin-bow in order to obtain Chladni's figures) had a remark- 

 able effect on a tall and slender gas-flame that happened to be 

 burning near. At the sound of any shrill note the flame shrank 



* Heat as a Mode of Motion, article 546 (second edition). The "Rede" 

 Lecture on Radiation, pp. 45 & 47. 

 t Communicated by the Author. 



