March 4, 1892.] 



SCIENCE. 



137 



into the reservoir ; the connectien of the bag with the outside air 

 will remain as before, and when the bag is full the only work ex- 

 ternal to the reservoir will be that of lifting 3.4 ounces one foot. 



When a balloon rises into the atmosphere, then, the gas does 

 not expand, and in so doing perform an enormous amount of ex 

 ternal work ; but it simply displaces the air. The amount of work 

 in this case would be very small indeed, and the consequent cool- 

 ing of the gas slight. The conditions are precisely similar to what 

 they were when we connected the bag with our reservoir having 

 the air under pressure. In rising, the balloon continually arrives 

 at a region in which the pressure is less and the expanding gas 

 simply displaces the surrounding air. Every cubic foot expan- 

 sion in the gas of the balloon at sea level displaces a cubic foot of 

 air at a pressure of thirty inches. If the pressure of the outside 

 air were suddenly diminished to ten inches, the work done would 

 be that of lifting a gas weighing one-third of the air at normal 

 pressure, or about .4 ounces to each cubic foot. This would cause 

 almost an inappreciable cooling in the gas. 



.\ very interesting point may be mentioned in this connection. 

 What became of the energy stored in the reservoir in the air com- 

 pressed to two atmospheres, after the air had expanded to normal 

 pressure in the reservoir and bag? Paradox. 



February 26, 1S93. 



The Loup Rivers in Nebraska. 



I AM grati6ed that my article of Jan. 39 possessed some interest 

 for so able an authority as Professor W. M. Davis of Harvard, 

 albeit, he is somewhat critical. 



My main propositions, and I think they will stand, notwith- 

 standing the objections of my critic, are these: — 



1. The Loup rivers were probably once "separate tributaries of 

 the Platte, all independent of each other, as roughly indicated by 

 the dotted lines on the map" (Fig. 1, p. 59, Science, Jan. 39, 

 1893). 



3. Pliocene lacustrine deposition along the Platte " crowded 

 the mouths of these tributaries eastward and made them coalesce 

 into a single large tributary." 



3. Headwater erosion "swept the upper courses westward by a 

 series of captures." 



Instead of my first proposition, Professor Davis ascribes to me 

 the postulate " that at the beginning of the current cycle of river 

 history the several branches of the Loup River all pursued inde- 

 pendent courses to the Platte." He makes definite my indefinite 

 " once," Jbut not in a way that I can accept. The plain inference 

 from my second proposition is that the period of separate existence 

 of these tributaries was in the Miocene. 



Whether that is equivalent to the "postulate" of Professor 

 Davis depends upon the definition of "cycle." The facts, as I 

 have read them in the field, are these: In Miocene times tribu- 

 taries of the Platte, now constituting the Loup system, were de- 

 veloped only to the stage of young rivers, not mature rivers, as 

 Professor Davis supposes. Then came submergence and partial 

 obstruction of their valleys; partial only, because the Pliocene 

 marls will not average more than fifty feet in thickness, not one- 

 fourth of the depth of the valleys. When Lake Cheyenne retired, 

 the rivers resumed business in their former channels, except near 

 the Platte, where the excessive deposition turned them eastward. 

 The silt in the Platte valley has been penetrated to the depth of 

 five hundred feet without reaching the bottom. 



Here then is a cycle of river history interrupted in its infancy, 

 and subsequently resumed. Its course was not half run when the 

 rivers were drowned, and, even now, after their emergence and 

 resurrection, they are still young rivers, with abundant vigor and 

 abundant opportunities for headwater erosion and river piracy. 

 If this series of events may be accounted a single cycle, notwith- 

 standing the Lake Cheyenne episode, then I can adopt the "pos- 

 tulate " as equivalent to my first proposition. 



It I understand him aright. Professor Davis does not raise any 

 objections to my second proposition. He does indeed argue against 

 a supposed contention of mine, which is not mine at all, namely, 

 that the coalescence of the lower courses into one Loup River was 

 due to headwater erosion. 



The effects which I did assign to headwater erosion were limited 

 to the "upper courses," as stated in the third proposition. Inspite 

 of all objections, that proposition seems to be reasonable and 

 valid. No region on this continent is more favorable for the study 

 of simple, unobstructed headwater erosion than these western 

 plains. The rivers are young. Great blocks of table lands lie yet 

 unbroken by drainage lines, and into these fresh ravines are con- 

 stantly eating back. The tertiary beds are soft and practically 

 homogeneou.'s, so far as resistance to erosion is concerned, so that 

 no question need be raised about dip, strike, folds, or alternations 

 of hard and soft strata. Upon such a terrane the Miocene rivers 

 established themselves with a south east course consequent upon 

 the slope to the southeast. The Rocky Mountain upheaval, to- 

 gether with excessive deposition along the Platte, changed the 

 slope to the north-east, transverse to the established direction of 

 the rivers. Cross-cutting and captures of westerly headwaters 

 was the natural result of this change of slope. 



The eastward tilt which the whole country got at the time the 

 Rocky Mountains were elevated also affected the development of 

 the main Loup. Without that upheaval the northern tributaries 

 would have been dammed back by the silt along the Platte, and 

 formed a series of swamps, instead of coalescing in a free-flowing 

 stream. 



That objection of Professor Davis, which is based upon the 

 "systematic location" of Prairie Creek "between two parallel 

 and larger rivers in a district of horizontal beds," is not serious. 

 In the first place, I never dreamed of ascribing it to headwater 

 erosion. It is obviously the result of Pliocene deposition crowding 

 the Loup so far from the Platte that subsidiary drainage was de- 

 veloped on the intervening space. In the second place, this latest 

 product, appearing upon the surface of a great mass of Pliocene 

 silt, cuts no figure in determining the primitive course of chan- 

 nels lying at the bottom of that mass of silt. 



Further criticisms from Professor Davis will be most welcome 

 L. E. Hicks. 



The Aboriginal North American Tea. 



In Science for Jan. 33, 1893, is an abstract of Bulletin No. 14, 

 United States Department of Agriculture, on "The Aboriginal 

 North American Tea," Ilex cassine, which recalls to me that dur- 

 ing our civil war, when the Confederate soldiers were encamped 

 in the vicinity of the Rappahannock River, especially during the 

 winter of 1863-3, that not only they, but also the inhabitants of 

 that region, used freely the leaves of the American holly tree, Ilex 

 opaca, in the preparation of a decoction as a substitute for China 

 tea. This species of holly is not only abundant in that region, 

 but grows to a large size, trees of eighteen inches in diameter and 

 over being not uncommon in the thickets bordering the low 

 grounds of the Rappahannock. 



I do not know how they came to begin the use of this decoction, 

 whether from a local handing down of the Indian custom of using 

 the cassena tea, as Wood styles the Hex cassine, or whether it may 

 not have been suggested by soldiers from Alabama, who were 

 numerous in the Confederate army, and who would be more likely 

 to know of the use the Creeks made of the leaves of the shrub 

 holly. 



In this connection the question arises as to whether any use was 

 made during our civil war of the leaves of the New Jersey tea, 

 Ceanoi 7ms -4merica?2Ms, which were used during the Revolution 

 as a substitute for Chinese tea. Jed. Hotchkiss. 



Staunton, Va., Feb. 24. 



AMONG THE PUBLISHERS. 



The laboratory course in psychology, by Dr. E. C. Sanford, 

 which is being published in parts in the American Journal of 

 Psychology, is to be issued at a later date in book-form. It is the 

 only practical course ever published. 



— Messrs. J. Wiley & Sons, publishers of scientific works, New 

 York City, have just issued the fourth edition of Thurston's 

 " Manual of Steam-boilers," and the fourth edition of his "Fric- 

 tion and Lost Work in Machinery and Millwork." These works, 

 like all others on their list, are kept under constant revision, and 



