lPRIl 9, 1886.] 



SCIENCE. 



329 



description of the arrow used, should be carefully 

 'reserved. 



As soon as possible, I shall publish an account of 

 he bows and arrows in the national museum, and. 

 hall be more than pleased to collate and preserve 

 he results of careful experiments as a basis of com- 

 parison with the archery of savages. It is generally 

 onceded that the archery clubs, with their much 

 letter artillery, achieve higher averages in shooting 

 han could be attained by the aboriginal bowmen. 



0. T. Mason, 

 Curator of Dept of ethnology. 



linithsonian institution, 

 March 31. 



Underground rivers. 



In an article in Nature (Jan. 14. p. 246) entitled 

 Curious phenomena in Cephalonia,' a former pupil 

 >f Ledger writes. " The sea runs into the land in a 

 tronsr stream, turning a water-wheel on the way, 

 ind disappears in the earth about a hundred yards 

 'rom the entrance. ... I imagine that this water 

 nust be converted into steam, which comes out 

 'ither at Naples or at Stromboli." Prof. Henry S. 

 Williams of this university called my attention to 

 ;his quotation, and to its indirect connection with 

 vhat follows. The writer, while passing through 

 Yucatan, Mexico, in 1870, saw a large stream run- 

 ling with torrential speed within a natural tunnel 

 not 'far from the seashore, and probably over one 

 lundred feet below the surface of the ocean. These 

 mderground rivers, which are said to be numerous 

 n the neighborhood of the city of Merida, are 

 called zanates (Thah-n'ah-tess) by the inhabitants of 

 Fucatan. I had time to' visit only one of these re- 

 narkable subterranean rivers. Its shaft-like en- 

 hance was adorned by a picturesque old Spanish 

 ivell-curb of stone, furnished with standards of 

 fancifully forged iron-work. Nothing on the surface 

 ndicated the existence of the vast cavern under the 

 monotonous and flat lowlands of the peninsula of 

 Yucatan ; and, though not a breath of air stirred, 

 the deafening roar of the torrent under our feet 

 L'ould not be perceived until we were fully inside of 

 the cave. . A rapid descent brought us to the level of 

 the pumps used for irrigating a very extensive ixtle 

 plantation ; and from here we could see, by the light 

 of our torches, the yellow foam of the waters upon 

 the undefined background of the chasm below. De- 

 scending still farther, the full stream could be seen 

 through a wide fissure in the limestone of the cave. 

 It had the rounded appearance of a stream flowing 

 horizontally under great pressure, ten or twelve feet 

 in diameter, and looking like a gigantic black icicle 

 lying on its side. This large volume of water plunged 

 with great swiftness into an unexplored and dark 

 "hamber with terrific roar, and producing noises 

 which resembled the hollow echoes of heavy explo- 

 sions heard now and then above the perpetual 

 umbling of the rushing water. A visit to this cave 

 'annot fail to produce a very deep impression, and 

 •iot unlike the feeling which renders so imposing the 

 mpleasant experience of an earthquake. 



The manager of the plantation informed me that 

 ,he mouth or entrance of this zanate was only 

 wenty-eight feet above the Gulf of Mexico ; and 

 ince my barometer indicated a descent of a hundred 

 nd forty feet, if the information was correct, this 

 tream was delivering, within forty miles from the 



seashore, a volume of fresh water about a hundred 

 and twelve feet below the level of the sea. The 

 temperature of the water was o2° F . and is said 

 to remain constant throughout the year. Only a 

 small portion of the stream was visible ; and the 

 direction of the current was N. 60° W. I could ob- 

 tain very little additional information in reference to 

 the other zanates, of which the natives speak with 

 almost religious reverence as " great miracles which 

 have always been as they are now." 



Since the velocity of the water, as well as the 

 form of its cross-section, can leave no doubt that the 

 delivery takes place under a considerable head, it 

 would be quite important to ascertain the location 

 of its source, and learn why this cave does not fill up 

 to within twenty- eight feet from the surfaoe, if the 

 stream communicates with the sea. This latter cir- 

 cumstance seems to prove that the elevation given by 

 the manager of the plantation may be incorrect ; 

 but, besides the fact that the belief in the great 

 depth of these zanates below the ocean is current 

 among the cultivated people of Merida, the manager 

 of the plantation insisted on the correctness of his 

 figures, which were obtained by the instrumental 

 surveys connected with the irrigation of his large 

 estate, the waste water from which runs into the 

 sea. It would seem desirable, therefore, to ascertain 

 through the columns of Science if any one else has 

 visited these zanates, and has satisfactory data 

 bearing upon this question. 



A study of the soundings made by the IT. S. 

 coast and geodetic survey upon the Bay of North 

 America : the erosions showed by the stereographic 

 model of the Caribbean Sea, made by Capt. J. R. 

 Bartlett, U. S. N. ; the gravimetric work conducted 

 by Professor Peirce of the coast survey ; and the 

 hydraulic problems connected with the delta of the 

 Mississippi River, — seem to involve problems related 

 to the Gulf Stream which make desirable a better 

 knowledge of these truly remarkable subterranean 

 rivers. E. A. Fuertes. 



Ithaca, N.Y., March 30. 



Note on the nocturnal cooling of bodies. 



An interesting application to this subject may be 

 made, by way of supplement, of the principles and 

 expressions contained in my letter on the tempera- 

 ture of the moon (Science, vi. No. 150). According 

 to these, the rate with which a body radiates heat is 

 to that with which it receives and absorbs heat from 

 a complete enclosure as ^ is to ^ . in which M = 

 1.0077, and eand 6 are the temperatures of the body 

 and of the enclosure respectively on the centigrade 

 scale. In this case we necessarily have for the 

 static temperature of the body, that of the enclosure 

 remaining constant, e=e' ; but, in the case of an 

 incomplete enclosure, the body, at the same tempera- 

 ture, radiates more heat than it receives and absorbs 

 from the enclosure, and consequently its static tem- 

 perature is less than that of the enclosure, since it 

 cools down until the rate with which it radiates heat 

 is equal to the rate with which it absorbs heat re- 

 ceived from the enclosure. 



In the case of a thermometer exposed near the 

 surface of an earth without an atmosphere, the 

 earth's surface would form the half of a complete 

 enclosure, since it would subtend a solid angle equal 

 to that of a hemisphere. In this case the thermome- 

 ter would receive no heat from the enclosure by re- 



