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THE POPULAR SCIENCE MONTHLY. 



the fall would be at least to 50 below zero 

 of Fahrenheit. " We see," says Professor 

 Langley, " if these results be true, that the 

 temperature of a planet may, and not im- 

 probably does, depend far less upon its 

 neighborhood to or remoteness from the 

 sun than upon the constitution of its gase- 

 ous envelope ; and, indeed, it is hardly too 

 much to say that we might approximately 

 indicate the constitution of an atmosphere 

 which would make Mercury a colder planet 

 than the earth, or Neptune as warm and 

 habitable a one." A much greater value 

 than has hitherto been accepted appeared 

 to be given by the observations to the solar 

 constant, amounting to one half more than 

 that determined by Pouillet and by Herschcl 

 near the sea-level, and even to more than 

 the recent values assigned by M. Viollc. 

 The bolometer observations at the summit 

 and base of Mount Whitney indicate a dif- 

 ferent distribution of solar energy at the 

 upper station from that which prevails at 

 the lower one. They also indicate, as the 

 author states in a communication to the 

 French Academy of Sciences, that only one 

 quarter of the solar energy which vivifies 

 the world is found in the familiar field of 

 the visible spectrum and the ultra-violet ; 

 and that the other three quarters are found 

 in the infra-red. Thus the action of our 

 atmosphere, and, as is inferred from the 

 observations, that of the solar atmosphere, 

 is to absorb the short rays more than the 

 long ones. The real color of the photo- 

 sphere is blue ; and " white light is not the 

 ' sum of all radiations,' nor even of all 

 visually recognizable ones, but a composi- 

 tion of the small groups of special rays, 

 which, starting from this essentially blue 

 sun, by virtue of their large coefficients, 

 and by a kind of survival of the fittest, 

 have struggled through the solar and ter- 

 restrial atmospheres to us, while others of 

 short wave-length have failed on the way." 



Infectious Consumption. Dr. Alexander 

 McAldowie has considered the much-debated 

 question whether pulmonary consumption is 

 an infectious disease in the light of his own 

 infirmary and private practice. lie is of 

 the opinion that it is infectious, although it 

 is not so frequently communicated by in- 

 fection as it would be were the lungs less 



well protected than they are against the 

 access of germs. He mentions four cases 

 where the wife, previously healthy, and with 

 no family history of tubercular disease, be- 

 came affected while attending to her phthisi- 

 cal husband, and two cases in which per- 

 sons suffering from the pneumonic form of 

 the disease appeared to communicate the 

 tubercular form to healthy persons. Phthisis 

 is not often communicated in this manner 

 by ordinary intercourse, because the germs 

 are sifted out in the air-passages by the 

 vibrating action of the cilia situated there, 

 and are removed by expectoration. The 

 germs floating in the air are, moreover, 

 commonly dry, and of feeble infective pow- 

 er. The lungs are liable to infection only 

 when the inhaled germs escape the filtering 

 action of the bronchi and reach the air- 

 cells, where they come in contact with a 

 surface highly favorable for their absorp- 

 tion. This happens only under exceptional 

 conditions. The parts of the alveoli most 

 exposed to the attacks of inhaled germs are 

 those near the entrance, at the points where 

 the small bronchial tubes lose their cylin- 

 drical character and become covered on all 

 sides with the cells ; and pathological ob- 

 servation has proved that these are frequent 

 starting-points in phthisis. 



Snbterraneous Effects of Atmospheric 

 Pressure. Hardly sufficient account has 

 been taken of the variations in the pressure 

 of the atmosphere as a force competent to 

 produce important effects within the earth 

 and on its surface. The pressure on a 

 man's body amounts to thirty thousand 

 pounds, and that exerted upon a table ten 

 feet long and five feet wide is equivalent to 

 more than one hundred thousand pounds. 

 In both these cases the pressure varies alike 

 on all sides, and changes are not directly 

 felt ; but the cover of an air-tight box, the 

 pressure in the interior of which could not 

 vary, would act very differently, and would 

 respond to the slightest changes. The 

 crust of the earth probably certainly 

 where cavities exist is like such a cover. 

 The consideration of this fact may help to 

 explain the connection which many persons 

 think they have found between earthquakes 

 and coal-mine explosions and low stages of 

 the barometer. A part of the weight of 



