25° 



NATURE 



\Jan. 15, 1 880 



The same may be said of the Pacific in its eastern part, where 

 alone the trades are regular. In the Western Pacific, as well as 

 in the Western Indian Ocean, I admit that air from the northern 

 hemisphere reaches to the equator and somewhat beyond in 

 January, but not that this tends to give the equator a lower 

 temperature in this month than in July. According to Dove, 

 the mean temperature of 10° N. in January is 77° - 2 ; of 10° S. 

 in July, 76°'!. 



So far as the temperature of the equator is concerned, the 

 southern is the dominant hemisphere, and the equator is certainly 

 cooled by winds coming from the south. If the equator is not 

 everywhere warmer in January than in July, this is caused by 

 the rainy season, which on the equator, and even a few degrees 

 north of it, generally coincides with the southern summer. 

 Where the rains are not very heavy, as, for example, on the 

 Isle of St. Thomas, West Africa, we have: January, 78°'3 ; 

 [uly, 75°'7 ; at Padang, Sumatra, where the rains are exceed- 

 ingly heavy all the year, there is scarcely any difference at all 

 between the months. Somewhat to the south of the equator, 

 where to the difference in the nearness of the sun is added a 

 much greater height above the horizon in January, we have — 



July- 



Rainy Sea?< 



Amboina, Molucca Islands j g^ ^ May (Q Augu ( 



Latavia, Java, 6" S 777 7S'S December to February. 



Ternambuco, Brazil, S° S. Soo 75'o April to July. 



si, by the first-rate observations of Eatavia, it is established 

 that, so far as 6° S., January is l°'l colder than July, because the 

 former is very rainy, while the latter has little rain. Even to 

 9° lat. N., July is colder than January, if the former has much 

 more rain, so for example — 



ISl rffic a!/ e N? and ° F °' W : I 79-9 7^5 March to November. 

 GondoVoro, Upper Nile, s°j 8r3 ^ April to August . 

 Freetown, W. Africa, 81° N. So - 4 77 'O June to October. 



Thus, in the lowest latitudes of the northern hemisphere, we 

 find difference; amounting to 5° - 6, while in the southern greater 

 differences than l"'l are not known, which may, to a certain 

 degree, be ascribed to the nearness of the sun in January. 



I think I have proved that, as to what we call the temperature 

 of the air (really that of the lowest stratum), it is, on the equator 

 and a few degrees north and south from it, far more influenced 

 by the yearly distribution of clouds and rain than by the different 

 amount of heat received from the tun. The result would be 

 different if we knew the temperature of the whole stratum of air. 

 The heating of the upper surface of the clouds by the sun, and 

 c pecially the heat liberated i.i the conden-ation of water must 

 give to the higher strata a superior temperature than that they 

 had in the dry season ; in other words, the decrease of tempera- 

 ture with elevation is much slower during the rains than in the 

 dry season, as was shown for India by Mr. Blanford. This is 

 true for other regions, and where the sky is cloudy and rains 

 abundant in the greater part of the year, the temperature of the 

 whole air may yet be higher than in drier climates, where the 

 soil and the lower stratum of air are hotter. 



I do not agree with Mr. Croll in what he states at the end of 

 his letter as to the effect of winds in cooling the equatorial 

 regions and rendering them habitable, as they would be too hot 

 for man without the cool air brought from the temperate regions. 

 1 think Mr. Croll has euormou ly over-stated the effects of wiuds 

 on the temperature of the equator. The extent of the tropical 

 zone is so great, its temperature so very near to that of the 

 equator, the winds which blow across it so gentle, that I consider 

 the effect of the winds from the temperate regions in directly 

 cooling the temperature of the equator to he nearly imperceptible. 

 The following is a good illustration: — Nowhere is the winter 

 temperature so low near the tropics as in Southern China, for 

 example, in January, Canton, 55°'6, Victoria, Hong-Kong, 

 59°'2. Yet Saigon, in Cochin China, but n° to the south of 

 Hong-Kong, and subjected to the full force of the north-east 

 monsoon from the China seas, has a January temperature above 

 77°. Clearly the thermal effect even of the cold winter monsoon 

 is scarcely perceptible farther south. 



I consider water to be the only direct cause of the mildness 

 and uniformity of equatorial temperatures, and this in three 

 ways — (1) by the great heat-capacity of water ; (2) by the clouds 



which interpise a screen between the sun and the surface of the 

 earth ; (3) by the evaporation of rain-water by the soil and 

 plants. 



The first cause is especially powerful on the ocean, while the 

 two latter act especially on land, even very far from the sea. If 

 it was not for the clouds and evaporation, how could we explain, 

 for example, the absence of great heat (hottest month, 78° - 6) at 

 IquitDs, on the Amazons, 4° S., and more than 1,000 miles from 

 the Atlantic, where the winds are generally weak ? 



As to the winds, I admit of their effect in this case ; but (1) in 

 causing ocean-currents, and thus removing the heated water from 

 the equator ; (2) in spreading the cold air from over the cold 

 currents over a greater distance. The latter is the cause of the 

 low temperature in the equatorial regions of the Eastern Atlantic 

 and Eastern Pacific. 



Where the sky is clear and humidity and rains deficient, very 

 high temperatures of the air are attained, even at a great dis- 

 tance from the equator (lo°-30°) and this notwithstanding winds 

 of considerable force blowing from cooler regions. So, for 

 example, the north winds blowing in the summer in the Sahara, 

 and coming from the cooler Mediterranean, are certainly stronger 

 than the trades of the ocean and yet do not prevent the desert 

 from attaining a higher temperature than know n in any equatorial 

 region. 



In the same number of Nature you committed an error by 

 giving the dates of freezing of the Neva in old style. The dates 

 in new style are : Mean day of freezing, November 25, earliest 

 October 28 (1S05), latest "(not quite certain), January 9(17111, 

 next latent December 26 (1826) ; mean day of opening, April 

 21, earliest, March 18 (1S22), litest, May 12 (1S10); number of 

 days open, 218, least, 172 (1852), greatest, 279 (1822). 



A. WOEIKOI' 



Sekpaleruaya 8, St. Petersburg, December 5-17, 1879 



Hearing through the Mouth 

 The principle of the so called "Audiphone," described in 

 Nature, vol. xxi. p. 243, is by no means a new discover), 

 although the application of it may be novel. It has long been 

 known that sounds may be conveyed to the auditory nerves 

 through the mouth when the drum of the ear is defective 

 in its action, although the principle has, perhaps, been little 

 acted upon by aurists. Mr. Rhodes's system is to press the edge 

 of a vibrating metal disk again-t the upper teeth, and "the 

 vibrations thus taken up by the disk are transmitted through 

 the teeth and bones of the skull to the auditory nerve." (?) Such 

 a remedy will, in many cares, be thought more inconvenient 

 than the defect, and it is by no means necessary thus to jar the 

 teeth and the bones. Although I am not deaf, some years ago I 

 pr.ieti-ed the listening to very feeble sounds through the mouth 

 instead of by the outward ear, at the recommendation of the late 

 Sir Charles Wheat-tone. The inducing cause was to verify by 

 experimert the true character and the notes of resultant tones, or 

 Tartini's tones, a'lout which no t.vo authors had agreed. Sir 

 Charles lent me one of his symphoniums — little instruments 

 made like his concertinas, except that they were blown by the 

 mouth directly upon the metal springs instead of by bellows. 

 According to his directions I stopped my ears lightly with cotton, 

 but pressed it into the concha with athurnb upon the lip of each 

 ear. The little instrument was supported by my third and fourth 

 fingers, leaving the notes to be touched by the first and second 

 fingers of each hand. By thus excluding external sounds I could 

 hear the deep and soft resultant tones to perfection ; the 

 instrument should not be tempered because they result from 

 coincident vibrations of the notes sounded above. Iu these 

 experiments I touched the symphonium as lightly as possible 

 with elongated lips, the cavity of the mouth receiving the sounds. 

 The teeth were covered by the lips. Wm. CHAPPELL 



Strafford Lodge, Oatlands Park 



Intellect in Brutes 

 The numbers of Nature containing the interesting dUcussion 

 on this subject have only lately reached us, and it is late to bring 

 forward anything on the question, yet the readers of Nature 

 will be interested in two instances of " calculation " on the part 

 of wild birds that I have noticed. Some years ago I was over- 

 looking a penguin "rookery" as it is called, at the Falklands, 

 and watching the goings on of the numerous colony below me. It 

 was breeding season, and the birds were sitting on their eggs on 



