206 Bibliographical Notices. 



plains why the Creator has multiplied in such a marvellous degree 

 the animalcules and microscopic plants with which water abounds. 

 Though regarded frequently as objects of disgust and forerunners of 

 disease, they are, in fact, necessary to the general harmony of nature. 

 It is to them we are indebted for the salubrity of waters which would 

 otherwise be injurious*. 



We proceed to state the circumstances which led to these inves- 

 tigations, as our readers will easily understand from them the nature 

 of the observations. M. Augustus Morren had analysed the water 

 of a great number of wells and fountains at Angers, and examined 

 the gases which it is capable of containing. He then experimented 

 on that of some neighbouring ponds, and he found that, habitually 

 impregnated with a large quantity of vegetable and animal sub- 

 stances, it held in dissolution, notwithstanding the contact of a per- 

 petually-renewed atmosphere, a gas frequently less rich in oxygen 

 than the water of the two rivers, Maine and Loire, which run near 

 Angers, and even than the water of the wells and fountains of the 

 country. 



After the admirable work of Humboldt and Guy-Lussac on Eudio- 

 metry, we know that in its normal state the running water of rivers, 

 or distilled water, well aerated, holds in dissolution about a 25th 

 part of its volume of oxygen and azote, in the proportion of 32 of 

 oxygen to 68 of azote. He was then greatly surprised, when, on a 

 fine day in the month of July, having analysed the air extracted by 

 ebullition from the water of a fish-pond, he found that it contained 

 56 to 58 per cent, of oxygen. This water had a green tint. He re- 

 peated the experiment, filtering it carefully to get it free from the 

 colouring matter, but the analysis gave him the same result. The 

 next day he analysed again the air derived from the water of the 

 same pond, taken at different times of the day. In the morning it 

 contained only 25 per cent, of oxygen, towards midday 48 per cent., 

 and at 5 in the afternoon 61 per cent., which was the greatest pro- 

 portion he ever met with. The volume of air contained was variable, 

 and increased perceptibly with the quantity of oxygen. The quan- 

 tity of azote remained constant, but the carbonic acid contained in 

 the water varied. 



These experiments convinced him that the solar light has an im- 

 portant part in these phsenomena, but that it is not the only cause 

 of them. Cold rainy weather succeeded, and the proportion of oxy- 

 gen was frequently less than 28 per cent. With the return of fine 

 weather the proportion did not exceed 34 ; but he found that the 

 green colour of the water had disappeared. In the middle of Au- 

 gust the water again became green and strongly oxygenated, though 

 in proportion to the light and heat of the sun. The green bodies 

 proved to be Chlomidomonas pulvisculus, Ehrenberg. 



The oxygenation of water is of course most important for those 



* The authors remark, that these relative effects were not even suspected 

 before. This however is scarcely correct. See the remarks of Sir J. E. 

 Smith under Con/, muralis, Eng. Bot. tab. 1554. — Ed. 



