FRAGMENTS OF SCIENCE. 



279 



Daguerre was born ; but it was left for him, 

 with the co-operation of Niepce de Saint- 

 Victor, to accomplish the object. Da- 

 guerre was not a chemist or physicist, but a 

 decorative painter, who when business was 

 slack was not above painting theater scenes 

 and panoramas, which had been introduced 

 into France by our Fulton ; and he deiived 

 much profit from a diorama which he ex- 

 hibited with Bouton from 1822 to 1830. 

 While thus occupied he met Niepce, a man 

 of scientific knowledge but none of business. 

 He told Daguerre of some experiments he 

 had made in heliography, and a proposal of 

 partnership followed in 1826. Niepce, how- 

 ever, never reached a practical result, but 

 died in 1833, leaving a son who continued 

 his researches. Daguerre in the meantime 

 had acquired some ideas in chemistry and 

 knew all Niepce's secrets, but was not able 

 to use them alone. He formed another alli- 

 ance with the son. In 1839 this younger 

 Niepce called Daguerre into his laboratory 

 and showed him a complete image fixed upon 

 a silvered plate — the first daguerreotype. 

 From this the photographic art has been de- 

 veloped by a succession of brilliant discov- 

 eries. No exact mathematical award of the 

 merit of the invention can be made between 

 the partners, but they must receive each an 

 undivided share alike ; but Daguerre has 

 certainly reaped the wider fame. The dis- 

 covery created a great sensation. In order 

 that it might be placed immediately at the 

 service of the public, the French Chambers, 

 on motion of Arago, awarded pensions of 

 six thousand francs to Daguerre and four 

 thousand francs to Niepce as the price for 

 which it should be made free. 



The Career of a Floating Bag. — Float- 

 ing bogs are very prominent features in 

 some of the lakes of Minnesota. They have 

 not, however, been found very abundant by 

 Mr. Conway MacMillan in the Lake of the 

 Woods. As developed, Mr. MacMillan says, 

 the floating bog comes to have some char- 

 acters peculiarly its own, due to its moving 

 about in the water and its removal from any 

 particular point of attachment. A redistri- 

 bution of its component plants takes place, 

 and the peripheral areas are specialized 

 from the central. A group of plants may 

 be distinguished at the water's edge, able to 



bear the lapping of the waves and enjoying 

 the higher illumination. At the center of 

 the island shrubs, or even small trees, may 

 become established. Drifting about from 

 one shore to another, touching at different 

 points, and frequently exposed to strong 

 winds while in transit, the bog becomes a 

 resting place for numerous varieties of light 

 seeds. It is, further, sometimes colonized 

 by the plants of the region near which it 

 may be situated. Thus the number of spe- 

 cies of plants established upon it tends to 

 rise ; and floating bogs of long standing are 

 scenes of very sharp struggle for existence 

 among a considerable number of alien 

 plants. The undulating movement commu- 

 nicated to the bog when exposed to wave 

 action loosens somewhat its tangled network 

 of roots and decayed organic substances, so 

 that the nature of its soil is modified. The 

 presence of the lake water underneath every 

 part of the formation keeps it cool and 

 moist beyond what is possible in an attached 

 morass. These various conditions are suffi- 

 cient to give the floating bog a population 

 distinctively its own. It often happens that 

 after floating for a season or two, or even 

 for a number of years, a bog is carried into 

 some angle or cove from which it does not 

 readily escape, and may become anchored 

 there. It is then subjected to the influences 

 of the new environment, and is modified ac- 

 cordingly. 



Limits of the Power of Ilearing. — Lord 



Rayleigh began a lecture at the Royal Institu- 

 tion on The Limits of Audition by observing 

 that one of the latest determinations of the 

 frequency of vibrations to which the ear is 

 sensitive gave the lower limit as twenty-four 

 complete vibrations a second, and the upper 

 as about twenty thousand a second. These 

 limits are, however, very ill- determined, be- 

 cause the matter depends largely on the 

 vigor of the vibration and the individual ear. 

 Old people do not hear high notes which are 

 audible to young persons, and the speaker had 

 reason to believe that babies hear notes which 

 persons twenty or thirty years of age can not 

 detect. Experiments on the extent of vibra- 

 tion necessary to audition were described, 

 which appeared to show that a vibration 

 having an amplitude expressed in centi- 

 metres by a fraction having eight for its 



