Proctor's Astronomical Lectures. 



15 



know that on our own earth life ceases in those upper 

 regions at the hight Coxwell and Glaisher reached, and 

 in Mars lire only of the lower kinds could possibly exist. 



THE ROTATION OF MAES. 



I have yet to make a few remarks about 

 Mars. I have told you the plauet has been 

 charted. Its period of rotation has also been 

 determined. It would seem strange that you could 

 tell the time taken by a plonet turning on its axis, ex- 

 actly, within a few seconds, or part or a second. You 

 see that spot in the middle of the planet. You could not 

 be certain, within a quarter of an hour, whether that 

 spot is in the middle of the planet. But if you note this, 

 you can observe it in the planet iu the second rotation. 

 If you are a quarter of an hour wrong in that case, that 

 q larter of an hour is divided between the two rotations. 

 The difference is only seven and a half minutes. That ia 

 divided into three rotations the next day, and so the 

 error is reduced to five minutes; and so on for a month, 

 until the error becomes smaller, and you can 

 let the plauet pass away for a year, so 

 that you can know when exactly it comes 

 back and how many rotations it has made in the in- 

 terim, and thus the error is still more reduced by rota- 

 tion after rotation, until in the course of many years 

 you get the time of rotation accurate within a second or 

 much less. It had been shown by a certain German 

 astronomer that the period of rotation of Mars was 24 

 hours 37 minutes and 23.J seconds, or thereabouts. Then 

 another German astronomer, Kaiser, improved on that, 

 and he made the period of rotation 24 hours, 37 minutes 

 and 22 6-10 seconds. Well, then, an English student of 

 astronomy, one who does not venture to call himself an 

 astronomer, an English student, Mr. Proctor, 

 thought he would try his hand at this problem. 

 [Applause.] And to his great distress he 

 found that his result was greater than the German's by 

 a whole tenth of a second that it should be 24 hours. 37 

 minutes and 22 7-10 of a second. Kniser thought it neces- 

 sary to go over his work and publish a paper on the sub 

 ject. From his paper I found he seemed to make out his 

 case very accurately indeed. Tiiere was a wonderful 

 amount of German care and labor, many details ; but I 

 found, strangely enough, two mistakes. He called the 

 years 1700 and l&CO leap years, whereas we know that in 

 the Gregorian caleudar they are not leap years, and 

 that made all the difference. And when that was 

 corrected, I found my theory of the planet was correct, 

 and the actual time it turned around in was 24 hours, 37 

 minutes and 22 7-10 seconds. It may seem to you un- 

 necessary to be so exact. But there is one important 

 question which may be solved by such information as 

 that. It has been found that our earth is rotating more 

 and more slowly as centuries go by. The moon liffs the 

 tidal wave; that tiddl wave acts as a brake, as it travels 

 in a direction contrary to that in which the earth 

 rotates, and slowly indeed our earth, ia losing 

 its speed. We cannot measure that chai.ga by 

 any ordinary clork, because our clocks are 

 set by the rotation of the earth. We time our clocks to 

 the transit of the stars. How can we answer a quest-ion 

 such as that except by having some true clock i Here 



is Mars, this small planet, a pocket chronometer, and 

 we can have that chronometer's time, and so soon as 

 we have her time we can compare with that our own 

 terrestrial clock. There are well-marked places on the 

 face of the planet, and there is this also, that the planet 

 has nothing to disturb its rotation. Tno sun is so far away 

 that the solar tides do not afl'jct it ; it has no moon, and 

 the oceans are not suited to the formation of a tidal 

 wave; therefore the change of the planet's rotation 

 would be insignificant. The plauet is a suitable clock 

 for getting at our earth's rotation. 



THE ASTEROIDS AND THE GIANT PLANETS. 



I now pass from these planets to the asteroids. There 

 are now known 134 of these minor planets. There is a 

 theory in the books that the asteroids are produced by 

 the bursting of planets. That ia not correct. Observa- 

 tions on the orbits which would result from such a catas- 

 trophe completely deinoliatx that theory. 



ORBITS OP THE OUTER PLANETS. 



Considering the giant planets, to which I next 

 we shall feel that they may be quite unlike this earth 

 on which we live. Consider the enormous size of 

 Jupiter. We are accustomed to consider him larger 

 than our earth: but it is not merely that; he ia 

 1,230 times lareer. Here ia a difference altogether too 

 great to be regarded as a difference of degree ; it ia 

 a difference of kind. Our conceptions of Jupiter are 

 necessarily different. We should expect it would be a 

 different kind of body from that on which wo live, and 

 we find clear evidence of that as we consider him. We 

 have views of the planets here, but they are not aa 

 clearly visible to this large audience aa I require. 

 I have better views, and I shall have the room 

 darkened and the views thrown upon the screen. 



As soon as you look on Jupiter you feel that you have 

 to deal with a body altogether different from Mars and 

 Mercury; altogether different from those which we hare 

 been dealing with. Compare these views with those of 

 the planet Mars, and you will see that there is no simi- 

 larity in the conditions. Iu Jupiter you have bands oi 



