SCIENCE-GOSSIP. 



weather, before it begins to freeze. Similarly, large 

 rivers emerging from great lakes at first assume the 

 thermal regime of the upper waters of the lake. 

 This matter has been admirably worked out by Dr. 

 Forster (Geogr. Abhandl. Wien, v.). The principal 

 effect lies in the equalising influence of the lake 

 waters, which are neither so cold in winter nor so 

 warm in summer as in a river of the plain, the 

 range of the monthly means being, as in the case of 

 the Rhone, at Geneva, much diminished. 



Streams, as they flow through a hilly district, 

 and rivers traversing mountain ranges, have for 

 obvious reasons, a cool temperature, and display a 

 limited and sometimes a very contracted range. 

 Mountain streams, according to Dr. Forster, are in 

 winter always warmer and in summer always cooler 

 than the air, the result being a contracted annual 

 range. Sir Joseph Hooker, when exploring the 

 Himalayas, found that the Tista, a river there com- 

 parable in its bulk of water to the Thames, varied 

 in the lower part of its mountain-course only ten 

 degrees in the year, and showed little or no daily 

 range (" Himalayan Journals"). When such streams 

 and rivers emerge into the full exposure of the 

 plains, they at once begin to raise their temperature 

 and to increase their daily range. The Tista 

 carries its cool waters far into the plains of 

 northern India, and the Brahmaputra retains its 

 coolness for a score of leagues after issuing from 

 the Himalayas into the broad valley of Assam 

 (Proc. Roy. Phys. Soc. Edin. xii). 



There remains to be considered the temperature 

 of still or stagnant waters, which comprise every- 

 thing between a splash or a puddle and a lake or an 

 inland sea. The road-splash, though exhibiting a 

 daily range approximating that of the air in the 

 shade, displays an unexpected tardiness in respond- 

 ing to the nocturnal falls of temperature. Thus, 

 for instance, in the middle of November I found 

 that whilst the air at sunrise was forty degrees, 

 the water of splashes, an inch deep, was forty- 

 three degrees, the air during the whole night 

 never having been above forty-one degrees. From a 

 series of carefully guarded experiments on bottles 

 of water suspended in the air and others fixed a few 

 inches deep in the ground, I concluded that at least 

 two-thirds of the excess of temperature at sunrise 

 of the splash as compared with the air was due to 

 ground-heat. This is an important factor in regu- 

 lating water-temperature, and goes to explain why 

 a river like the Thames will in summer, during 

 a sudden spell of cool weather, often preserve 

 for days a temperature higher than the air 

 maximum. 



A ditch about nine or ten feet across and a few 

 inches deep has a daily range about two-thirds that 

 of the air in the shade ; a pool twenty to thirty feet 

 wide and a foot deep, a daily range about half that 

 of the air ; whilst a large pond, four or five feet deep, 



has a range about one-fourth that of the air. These 

 remarks refer to surface-temperatures in sunny 

 summer days, and it may be said that surface- 

 heating is characteristic of still waters. It is far 

 more marked where a ditch or a pond is well 

 stocked with plants. Thus, a ditch of this kind in 

 a broiling afternoon will exhibit a difference of nine 

 degrees of temperature in as many inches of depth, 

 and a large pond, four or five feet deep, will be as 

 much as eleven or twelve degrees warmer at the 

 surface than at the bottom. We, therefore, perceive 

 that in its marked surface-heating a pond differs 

 greatly from a river, and as far as its upper waters 

 are concerned, it is in sunny weather always warmer 

 than the river. Thus I found the ponds in the 

 parks around Kingston to be two or three degrees 

 warmer than the Thames in March, three to five 

 degrees in April, and six to twelve degrees between 

 May and August. 



Ponds also differ from rivers in their marginal 

 heating, which is only to be observed in any 

 amount in a very sluggish river. In the instance of 

 a pond in this climate, three or four feet deep, and 

 full of aquatic plants, the following temperatures 

 would be typical of a hot summer afternoon ; 

 seventy degrees at the bottom, eighty degrees 

 at the surface, and eighty-five to ninety degrees at 

 the margins. ''Daily range" is another varying 

 feature in pond-temperature. During fine summer 

 weather the pond just mentioned would have a 

 range in the twenty-four hours of about fifteen 

 degrees at the edges, about seven degrees at the 

 surface, and only one degree at the bottom. Such 

 are some of the leading characteristics of pond- 

 temperature, but since no two ponds possess 

 exactly the same thermal regime, the determining 

 conditions being almost infinite in their variety, 

 each will differ from the rest in important details 

 and will require a separate study. Space does not 

 permit of the endeavour to bring these facts of 

 observation into harmony with the habits, stations, 

 and areas of distribution of aquatic plants ; but I 

 can recommend no better plan for the training of 

 the powers of observation than to map out a small 

 pond, fix the position of its plants, note its tempera- 

 ture, and carefully record its physical and floral 

 history during the four seasons of the year. (The 

 writer's observations form the framework of this 

 paper, and the Fahrenheit scale has been em- 

 ployed.) 



6, Fairfield West, Kingston-on-Thames. 



Messrs. Phillip and Sons, of Fleet Street, 

 have recently published for the Government of 

 Western Australia a " Geological Sketch Map " of 

 Western Australia. The map is clear and well 

 printed, and the distribution of various metals 

 indicated. The scale is 1 = 3,000,000, or nearly 

 fifty miles to the inch. 



