272 



HARDWICKE'S SCIENCE -GOSS IP. 1 



[Dec. 1, 1867. 



differs from the typical forms described by Shadbolt, 

 both in its large size, more conspicuous venation, 

 and the curious band apparently girding and con- 

 stricting the angles ; but as it has, I believe, been 



Fig. 286. Amphitetras ornata (?), var. /3 x 



400. 



only found in AlgoaBay guano, 'it would be rash to 



make it a new species. It may possibly be the 



sporangial state of Amphitetras ornata. (Fig. 284 > 



x 400diam.) 



Norwich. Fred. Kitton. 



TEMPERATURE OF LAKES. 



AMONG the communications lately made to the 

 Academy of Munich are some observations 

 by Herr v. Schlagintweit on the temperature in the 

 deeper parts of the Starnberger See and the Chiem 

 See. A few observations on these measurements 

 will not be out of place, as they prove, in an un- 

 expected manner, that the Starnberger See, not- 

 withstanding its having an influx and outflow of 

 water, is sufficiently deep and large to be perfectly 

 cold at the bottom. 



In the salt lakes of Thibet (which first gave rise 

 to investigations being made in the above-named 

 Alpine lakes, for the sake of comparison) there is 

 this peculiarity, that except on days when the fall 

 of snow is at a minimum, there is no influx of water. 

 Moreover, while the appearance of the surrounding 

 country makes it evident that these lakes had once 

 an in- and out-let, as well as a much higher level, 

 now the surface lies lower than the ancient outlet : 

 the gradual drying up, too, is plain enough, as is 

 also the relative increase of the saline constituents 

 — a circumstance of course dependent on the les- 

 sening of the amount of water, for the continual 

 evaporation is much too great to be replaced by 

 the rainfall. 



In the large Atlas of his travels, the author has 

 given five illustrations of the scenery surrounding 

 these salt lakes— a perfect waste, but not without a 



certain grandeur. The illustrations are accompanied 

 by the necessary topographical explanations. 



His account demonstrates that the maximum oi 

 density (differing with the amount of salt contained 

 in them) is reached in lakes which are situated at 

 great heights above the sea, but which are sunk in 

 depressions, in which there is so little difference in 

 the warmth of the ground strata, that the balance 

 of the temperature remains undisturbed. It is well 

 known that water (unlike other fluid bodies) con- 

 tracts during the process of cooling, until it reaches 

 the freezing-point (distilled water, however, ceases 

 to contract at 4° Cent.), and that it again expands 

 as it gets colder : if it contains salt, this greatest 

 contraction, or maximum of density, commences at 

 a somewhat lower temperature. 



Now, what relation has this to the distribution of 

 temperature in the Alpine fresh-water lakes, which, 

 besides, experience a considerable variation in the 

 amount of water, owing to their having both an 

 inlet and a means of escape ? 



According to Professor Jolly (whose careful 

 observations, made much earlier than those of our 

 author, were confined to the small very deep lakes 

 of the Eastern Bavarian Alps) the temperature at 

 the bottom of the Konigs See (742 feet), and of the 

 Walchen See (852 feet), registers 5'3° and 5-2° Cent. 

 Herr v. Schlagintweit chose larger lakes for his 

 experiments. He found that in the Starnberger 

 See, in which the inflow of water is relatively small, 

 the temperature of the bottom (though only 406 feet 

 from the surface) betrayed "the maximum of 

 density," or, in other words, the water is as cold as 

 it can be. The conduction of heat from the ground 

 strata, or in some instances by springs, may in the 

 course of the year tend to modify this force of 

 greatest density (3'5° Cent.), but it could never, it 

 would seem, annul it altogether. 



In the Chiem See the result was different, partly 

 on account of the greater change of water, and 

 partly because the depth is very much less — 273 feet 

 only, as determined by Von Schlagintweit, more 

 than 130 feet less than that of the Starnberger See. 

 It may be mentioned, en passant, that in RiedelPs 

 lake map, the depth is given at 504 feet, which is 

 also the amount in the later map of Statzner, — a 

 difference which can scarcely be accounted for by 

 any change of bottom in the lake basin itself, 

 though Riedell's measurements were made more 

 than half a century ago, in 1810. The temperature 

 of the water in the Chiem See was 7'1° Cent., a 

 trifle colder than that registered at an equal depth 

 in the Starnberger See, but far from reaching the 

 temperature of maximum density. 



These determinations of the temperature at great 

 depths, are not without significance in regard to the 

 conditions under which the fish of fresh-water lakes 

 live. Similar observations made in other still larger 

 lakes would be exceedingly interesting, because the 



