Daguerre was born; but it was left for him, with the co-operation of Niepce de Saint-Victor, to accomplish the object. Daguerre 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 derived much profit from a diorama which he exhibited 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, however, 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 alliance 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 developed by a succession of brilliant discoveries. 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 discovery 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 Bog.—Floating 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 characters peculiarly its own, due to its moving about in the water and its removal from any particular point of attachment. A redistribution 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 species 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 communicated 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 sufficient 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 accordingly.
Limits of the Power of Hearing.—Lord Rayleigh began a lecture at the Royal Institution 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, because 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 vibration necessary to audition were described, which appeared to show that a vibration having an amplitude expressed in centimetres by a fraction having eight for its
