194 



KNOWLEDGE 



[October 1, 1892. 



of having to wait several days for a permanent condition of 

 temperature to be established, we should have to wait 

 several centuries. There would then still be one other 

 diii'ereuce between the two cases. Owing to the high con- 

 ductivity of the iron, the surface SF would be a few 

 degrees above the temperature of the outside air, while 

 the surface of the clay would be almost exactly equal to it. 

 This difference would depend upon the radiating capacity 

 of the surface SF. In this respect our earth resembles 

 the clay ; in other words, the radiating and absorbing 

 power of the surface SF so far exceeds the conductivity 

 of the long bar of clay that the temperature of the surface 

 depends practically entirely upon this radiating and 

 absorbing power, and will be the same whether the 

 temperature of CE is 0° C. or 1000° C. 



Suppose now that the temperature of CE should be 

 permitted to fall to 500°. Since the temperature of SF 

 still remains at 0°, we should now be able to advance twice 

 as far from F before we should reach the temperature of 

 boOing water. 



Applying this experiment to the case of our earth, let us 

 assume that half of the free water of the planet is at 

 present underground, and that all the microscopic cavities 

 that are not too hot are already filled with water. When 

 the internal temperature of the earth is lowered to one-half 

 of its present figure, there will, other things being equal, 

 be nearly twice as much space for the underground water, 

 and as a result we may expect that our oceans will dis- 

 appear, learaig our earth a warm but arid desert. Indeed, 

 this might occur at an earlier date, since at the greater 

 depths water would remain in the liquid form at a higher 

 temperature. 



WiLLi.Uii H. Pickering. 



Arequipa, Peru, 



Ai(!imt 6tli, 1892. 



P.S. — In printing my letter in the June number the 

 word if has been left out ; it makes a very material dif- 

 ference in my meaning. What I wrote was, " In the case 

 of this planet (Mars), however, we have good reason for 

 thinking that if it formerly had extensive oceans upon its 

 surface, that tiy the gradual cooling to which it has been 

 subjected there has been room formed for them in its 

 interior." 



[I agree with Prof. Pickering as to the increase in under- 

 ground temperature being probably slower in the body of 

 Mars than in the earth. 



The great range in the mean temperature in passing 

 from the earth's equatorial to its polar regfons shows that 

 if it were not for heat derived from the outside the whole 

 surface of the earth would have a mean temperature below 

 the freezing point of water. No amount of atmosphere could 

 increase theheatof the surface derived directly* from the sun. 

 One might as well expect to hasten the cooking of a joint 

 before a fire by covering the joint with a glass shade or 

 with a blanket, and we may be sure that the heat derived 

 from the outside by the surface of Mars is, area for area, 

 less than that derived by the earth's surface from the sun 

 in a proportion which varies with the inverse squares of 

 the distances of the two planets from the sun. If, there- 

 fore, as Prof. W. H. Pickering assumes, " the internal 

 temperature of the earth has lui injhiencc irhnicriT upon our 

 climate, the mean temperature of even the equatorial 

 regions of Mars must be far below the freezing point of 

 water. — A. C. Eanyard.] 



THE CRETAN LABYRINTH. 

 To the Editor of Knowledge. 



* TliougU an atmosphere which ivas trausparent to short wave- 

 lengtlis but absorbed long- wave lengths would tend to accunuilate the 

 lieat of the surface by preventing the return from the earth's sui'facc 

 into space of long wave-lengths, corresponding to heat of low 

 teni])craturc derived from solar radiation of shorter wave-length. 



Dear Sir, — That there was some kind of a maze or 

 labyrinth at Cnossus in Crete need not be doubted, as 

 there are coins or tokens of Crete with the device of a 

 labyrinth impressed upon them. Several of these coins 

 are displayed in the glass cases accessible to the public in 

 the British Museum. There is also, of course, the myth 

 about Theseus entering the labyrinth by the help of a 

 thread given him by Ariadne, when he slew the Minotaur 

 or Man-Bull who lived in the centre, and put an end to 

 the cruelties [practised by the monster. This legend, 

 beautiiul enough when taken in the anagogic sense, was 

 probably in existence before tlie maze shown on the coins 

 took any definite shape, or it may be that several successive 

 mazes were built and kept as long as any profit could 

 be made out of those who came to \isit them. I mention 

 this because some of the mazes shown on the coins are 

 circular, while others are rectangular, although the twists 

 and turns are practically the same in both plans. Now, 

 unfortunately, the labyrinths depicted on the coins are 

 apparently of such a simple character that anyone could 

 find his way to the centre and out again by the simple 

 process of following his own nose, because the maze seems 

 to consist of a roundabout path, leaving at no point any 

 choice of routes to the explorer. 



It has occurred to me that the device on the coins was 

 never intended as a map or plan of the labyrinth, but only 

 as a key or clue to the right path, leaving out the wrong 

 ones. By taking the maze as shown on the Cretan coins, 

 and treating the circular dividing walls as tlouliU , and each 

 containing a passage of the same width as the road shown 

 on the coins — in fact restoring the design to that shown on 

 the diagram accompanying this paper — one can see 

 that penetrating the maze to the very centre by the nearest 

 road and at the first attempt would be a matter of very 

 serious difficulty. Some of your younger readers will find 

 it not quite easy to trace the white path with the point of 

 a bone knitting needle ; or, if they take the trouble to 

 trace the maze large on the sea sand, they will find that 

 their companions not in the secret will get a good deal of 

 exercise before arriving at the centre. They must remember 



