February 24, 1888.] 



SCIENCE. 



tion, cannot be modified by the contraction-works : for their effect 

 •on the distribution of velocities in the bend below, it is only neces- 

 sary to point to the portion of the river below Baton Rouge. 

 Here the conditions prescribed for a regularized river obtain in 

 greater perfection than can possibly be realized on the river above. 

 Yet in this ideal stream the distribution of velocities follows the 

 cart-wheel analogy as closely as anywhere else. 



To sum up, the effect of the contraction-works on a shoal, upon 

 the conditions existing in the bend below, is simply nothing, — 

 nothing as to the distribution of velocities, and nothing as to the 

 amount of sediment carried. 



In the face of this conclusion, the changes required by our hypoth- 

 ■esis, before it agrees to stop the caving, are quite discouraging. 

 It asks nothing less than the complete reversal of present condi- 

 tions. It requires that the restraint of a fundamental hydraulic law 

 be removed, so that the water may move at the same velocity at 

 bottom and surface. It demands that the rapid currents along the 

 caving banks be checked, and the sluggish ones on the other side 

 quickened ; that sediment shall be deposited in places whence it is 

 now removed, and removed from those where it is now deposited. 

 These revolutions of the river's regimen, as results of works at a 

 ■distant point, and which have, as has been shown, no effect upon 

 the conditions to be changed, are severally and equally impossible. 

 The greatest actual velocity will be found, as now, in front of the 

 ■caving bank. If the lesser velocity at the contraction-v/orks be 

 sufficient to produce scour there, the greater velocity at the point 

 of caving must also scour and the caving continue. If the velocity 

 along the caving bank correspond to saturation, so as to prevent 

 •caving, the lesser velocity on the shoal must allow deposits, and 

 navigation will be injured. 



The disparity in velocities is utilized by steamboats, the down 

 boats being assisted by the rapid currents in the bends, while the 

 up boats take advantage of the slack water on the otlierside. Uni- 

 form motion all the way across would retard the former preceptibly, 

 and the latter fifty per cent. It is now difficult to get up stream 

 enough pieces to accommodate the down-stream traffic. With uni- 

 form motion, it would be impossible. Navigation will suffer by the 

 most cautious bestowal of such benefits. 



A more general view leads to the same result as the local one. 

 Suppose the channel to have been regularized from Cairo to Baton 

 Rouge as completely as it now is below the latter point. In this 

 conduit, the water supplied by its tributaries is to flow under the 

 conditions that it shall always have the normal charge of sediment 

 due to the velocity, and that it shall neither erode the channel nor 

 make any deposits therein. No sediment being derived from action 

 on the bed, the supply must come entirely from the tributaries. 



The tributaries differ widely in their turbidity. The IVIissouri is 

 the largest silt contributor, furnishing much more than all the others 

 together. After it, but still classed as muddy, come the small 

 •streams on the east side above Memphis, the Arkansas and the 

 Red. The Ohio, St. Francis, White, and Yazoo are comparatively 

 clear. If our regularized channel be adapted in size to carry Ohio 

 water without scour or fill, deposits must result when the Missouri 

 predominates. If the channel be such that Missouri water can be 

 carried without loss or gain of sediment, scour and caving must be 

 expected when the supply is mainly from the Ohio. If a mean be 

 taken, the scour and fill will alternately occur, which is simply a 

 relapse into the present difficulties. No natural adjustment by 

 mixture is possible, since the streams named have drainage areas 

 lying in widely different latitudes, and it is rarely that their rises or 

 floods are co-incident. 



Suppose, again, that the corrected channel just below Cairo is 

 filled to a certain level with just the right mixture of Ohio and Mis- 

 souri water, having the normal charge of sediment due to its 

 velocity, and carrying it without loss or gain. A slight rise comes 

 out of the Ohio. Bringing an insufficient supply of sediment, it re- 

 duces the degree of saturation in the trunk stream. In order that 

 scour and caving may not begin, this addition of water must be 

 accompanied by a decrease of velocity and a rise of surface. If 

 the rise, on the other hand, comes from the Missouri, the case is 

 reversed, and, in order to prevent deposits and shoals, the velocity 

 must be increased without a corresponding rise in surface. To 

 realize either set of conditions requires an inverse ratio between 



velocity and slope, which is a blow at the fundamental law of the 

 universe, that of gravitation. These contradictory requirements 

 are repeated all along the river's course. The Forked Deer, Obion, 

 and Wolf Rivers must produce an effect on the main stream directly 

 the reverse of the St. Francis ; the Arkansas, of the White ; and the 

 Yazoo, of the Red. The velocity of the river must conform to the 

 supply of sediment, or the hypothesis will be violated. The supply 

 of sediment is fortuitous : hence chance must take the place of 

 hydraulic laws in controlling the flow of the water. 



There never has been a day in the known history of the river 

 when caving was not in progress. The amount of sediment requi- 

 site to produce normal saturation and prevent caving must 

 therefore be greater than the river has ever before carried. The 

 demand is, that the river be made muddier, and kept so. How as 

 to supply ? Of the present contributions, a considerable part is to 

 be cut ofi by the cessation of caving and scour, which are promised 

 as results of the improvement. The tributaries remain ; but of 

 these, the only one worth considering, the Missouri, is already under 

 improvement. The result of that improvement, if successful, will 

 be a fixation of its bed, and a large reduction of its output of sedi- 

 ment. The maintenance of even the present supply of sediment in 

 the trunk stream involves the degradation of the tributary. If the 

 Mississippi is to be improved on such principles, the regulation of 

 the Missouri must be stopped at once. 



We see, that, while the demand for sediment is increased, the 

 supply is largely reduced. A scheme of improvement, the vital 

 feature of which is the production and maintenance of increased 

 muddiness, promises as its results changes which must largely re- 

 duce the muddiness. Surely this is necromancy on a large scale. 



The saturation hypothesis, whether true or false, and following it 

 the anti-revetment theory and plan of improvement based thereon, 

 must be entirely rejected so far as the Mississippi River is con- 

 cerned ; because the conditions under which it is claimed to act 

 cannot be produced or maintained ; because uniformity of velocity 

 in any cross-section, or from one section to another, is impossible, 

 either in natural or regulated channel ; because the volume of water 

 which controls the velocity, and the supply of sediment, the two 

 factors which determine the saturation, are now practically inde- 

 pendent, and in a regulated channel become absolutely so, thus 

 making the combination of the two to produce normal saturation 

 a matter of chance and not of law ; finally and principally, because 

 the hypothesis contradicts and defeats itself in that it requires an 

 increased supply of sediment to produce results which, if realized, 

 must make this supply a constantly decreasing quantity. 



If the caving of banks is to be stopped, it must be done by means 

 outside of the contraction-works, since the latter cannot produce 

 the slightest diminution of caving. That they will greatly increase 

 it, may be strongly argued both from theory and experience; but 

 such is beyond the present purpose. Smith S. Leach. 



MENTAL SCIENCE. 

 A Second Laura Bridgman. 



The recently issued report of the Perkins Institution for the 

 Blind, where Laura Bridgman has spent fifty years of her life, adds 

 another most interesting and promising record to the accounts of 

 persons afflicted with this double infirmity. The number of per- 

 sons deprived of both sight and hearing is larger than is commonly 

 supposed, and gives no sanction to the common belief that the loss 

 of one sense insures an unusually strong development of the others. 

 From a psychological point of view, the value of such cases depends, 

 first and chiefly, on the age at which the senses were lost, those 

 cases being the most suggestive and valuable in which the loss is 

 earliest; secondly, upon the degree of blindness and deafness, as 

 well as the rapidity with which these senses lose their function, the 

 most instructive inferences being deducible from cases in which the 

 loss is total ; and, thirdly, from the completeness and accuracy of 

 the record of the person's capabilities and achievements at the vari- 

 ous periods of life, and especially during early childhood. In all 

 these respects the case of Laura Bridgman is a most phenomenal 

 one. Her life-history is to the psychologist most fruitful of hints 

 and suggestions, throwing clear light upon questions otherwise 



