The St. Johns herald., 1892-05-19
How Long can the Earth Sustain
 Life?

heat goes on, the gaseous parts vii
 turn into liquids, and as the pro
 cess is still further protracted, tn
 liquids will transform into solids
 Thus we look forward to a timt
 when the radiation of the sun car
 be no longer conducted in conform
 ity with the laws which dictate the
 loss of heat from q gaseous body
 When this state is reached the sur
 may, no doubt, be an incandescent
 solid with brilliance as great as is
 compatible with that condition, but
 the further loss of heat will then
 involve loss of temperature. At the
 present time the body may be so far
 gaseous that the temperature of the gun remains absolutely constant. It
 mav even be the case that the tenn perature of the sun, notwithstand- ing the undoubted loss of heat, is absolutely rising.
 It is, however, incontrovertible that a certain maximum tempera- ture having been reached (whether we have yet reached it not we do not know), temperature will then necessarily decline, There is cer- tainly no doubt whatever that the sun, which is now losing heat, even if not actually failing in tempera- ture, must, at some time, begin to lose its temperature. Then, of course its capacity for radiating heat will begin to abate. The heat received by the earth from the great center of our system must, of course, de- cline. There seems no escape from the conclusion that the continuous loss of solar heat must still go on, so that the sun will pass through the various stages of brilliant in candescence, of glowing redness. of dull redness, until it ultimately be- comes dark and non-luminous star. In this final state the sun literally joins the majority. Every analogy would teach us that the dark and non-luminous bodies Tn the universe are far more numerous than the brilliant suns. We can never see the dark objects, we can discern their presence only indirect ly. All the stars that we can see are merely those bodies which at this epoch of their career happen for the time to ba so highly heated as to be luminous
 There is thus a distinct limit to mans existence on the earth, dic- tated by the ultimate exhaustion of the sun. It is. of course, ques- ton of much interest for us to spec nlate on the probable duration of the suns beams in sufficient abun- dance for the continued mainte- nance of life. Perhaps the most reliable determinations are those which have been made by Professor Langley. They are based on hls own experiments upon the intensity of the solar radiation, conducted under circumstances that give them special value. I shall endeavor to | give a summary of the interesting results at which he has arrived. The utmost amount of heat that it would ever have been possible for the sun to have contained would supply its radiation for 1S,0O0,OO0 years at the present rate. Of course. this does not assert that the sun, as a radiant body, may not be much older than the period named. We have already l seen that the rate at which sun- beams are poured forth has grad ually increased as the sun rose in In the early times the quantity of sunbeams dispensed was much less per annum than at present, and it is, therefore, quite possible that the figures may be so enlarged as to meet the require ments of any reasonable geological demand with regard to past dura- tion of life on the earth.
 It seems that the sun has already about four-fifths of the