disk made six little separate voltameters each with its own pair of insulated leads. By uniting more or less of these leads outside the dish, the voltameter might be made to comprise any or all of the couples of electrodes, thus enabling a considerable range of electrode area to be at command, as shown by the preceding table. Over this sextuple yoltameter there rested a glass bell 7cms in diameter, terminating after 10cms of elevation in a vertical glass tube of uniform bore 37.5cms long and about 0-6cms internal diameter, closed at the top by a rubber tube and clamp. This tube was graduated for volume by comparison with a burette and found to have a capacity per linear centimeter from several measurements of 0.2684 ± 0·002 c. c. In using the instrument, the tube and bell were filled with solution and gas electrolytically generated until the latter stood at a certain mark near the top. All being ready, the measured current was then passed through the apparatus for a noted interval, at the end of which the length of tube occupied by gas was measured downward from the fiducial mark. as In the condenser method the connections were shown in the diagram: where A is the adjustable condenser, V the voltameter with commutators ce for connecting the separate couples of plates in multiple, B a Cardew voltmeter, and 7 l the leads to the dynamo. B Under these conditions we know that the absolute quantity of current passing through the voltameter assuming that the periodic variation of electromotive force follows the sine law: where Q is the absolute quantity of electricity that traverses the voltameter in time t; è is the mean alternating potential difference as indicated by the Cardew voltmeter B; k is the capacity of the condenser A in microfarads; and n is the number of alternations per second. This formula is thus independent of the resistance of the voltameter, which is quite negligible under these conditions. If V, be the volume of gas at zero Centigrade theoretically decomposed by a continuous cur rent c in absolute measure equivalent to the passage of this quantity Q, we have c = n π е k × 10−7 and V5·43 n e k t × 10−7 (2) (3) Besides the Cardew voltmeter steady potential indication, a quadrant electrometer, not shown in the diagram, with its needle connected to one pair of quadrants, was employed to measure the potential difference at the voltameter terminals and thus indicate its mean resistance. The preceding table gives the results of 10 measurements. The volume of the gas is corrected for temperature, but no correction is introduced for the barometric pressure or the tension sustained by the gas in the tube. The condenser used was adjustable from 0.001 up to 5 microfarads, and from absolute determinations is probably accurate to at least 0.5 per cent. The last two columns show that The trials Nos. 13, 14 and 15 were taken without condenser, and with non-inductant resistances in its place. In trial No. 13 this resistance was a length of fine platinum wire offering 720 ohms (hot). In trial Nos. 14 and 15 the resistance was a 96 volt 10 candle-power Edison lamp offering 230 ohms resistance at equivalent illumination. În calculating the current strengths for these three observations, the resistance of the voltameter itself was required. It was measured in two ways: 1st, by means of the quadrant electrometer and the potential differences it indicated on the known resistance and on the voltameter; 2d, by rapidly substituting a non-inductant resistance alternately with the voltameter in the lamp circuit and adjusting this resistance until the illumination was equal in both cases. These two methods concurred in showing the resistance of the voltameter to be 30 ohms, and the maximum resistance it offered through the whole series was 35 ohms. The table shows that When the current density per sq. cm. of either elec- 20.9 59.3 The per centage of calculated gas actually liberated was: 52 These results, corroborated by several previous series, go to show that for a rate of alternation of 200 per second and currents of between 01 and 0.35 ampères the quantity of gas generated by an alternating current in a voltameter is approximately equal to that generated by an equal continuous current when the mean current density at the surface of the electrode is above 50 ampères per sq. cm. of each; that below that density the quantity of gas developed rapidly diminishes, and that below 1 ampère per sq. cm. soon disappears. Also that the resistance of a voltameter with very small plates traversed by an alternating current is much less than that it would offer to an equal continuous current. Were this not the case, the resistance of a voltameter for alternating current measurements might for many purposes prove prohibitively great. ART. XLVII.—Remarks on the Fauna of the Great Smoky Mountains; with Description of a new species of Redbacked Mouse (Evotomys Carolinensis); by DR. C. HART MERRIAM. THE fauna of the higher portions of the southern Alleghanies remained almost unknown until 1870, when Prof. E. D. Cope published a paper on the subject.* His bird notes were made so late in the season (in August and September) as to include the beginning of the fall migration and hence are without value so far as concerns the faunal position of the region. Among mammals, he recorded the Red Squirrel and Canada Lynx as inhabiting the higher mountains. A single species of Salamander, the northern Desmognathus ochrophæus, was found on the high peaks of the Black Mountains. The botany of the region received considerable attention, but sixteen years passed after the appearance of Prof. Cope's paper before anything of importance was contributed to our knowledge of its vertebrate fauna. In 1886 Mr. William Brewster published the results of a very brief visit, made at the beginning of the breeding season of birds, to the mountains of western North Carolina (The Auk, iii, 1886, 94-112; 173-179). * Observations on the Fauna of the Southern Alleghanies. Am. Nat. iv, 1870, pp. 392-402. On the higher summits Mr. Brewster found breeding in abundance such northern birds as the Winter Wren, Golden-crested Kinglet, Red-bellied Nuthatch, Junco, Solitary Vireo, Olivesided Flycatcher, Red Crossbill, Pine Linnet, Black-throated Blue Warbler, Blackburnian Warbler, Canada Flycatching Warbler, and several others. He found the region separable into the Canadian, Alleghanian, and Carolinian Fauna, concerning which he says: "The boundaries of these divisions are determined chiefly by elevation, the Canadian occupying the tops and upper slopes of the higher mountains down to about 4500 feet, the Alleghanian, the mountain sides, higher valleys, and plateaus between 4500 and 2500 feet, and the Carolinian everything below the altitude last named." Two of the Canadian birds, namely the Junco and the Blueheaded Vireo, were found to be distinguishable from their northern representatives, and hence were subspecifically separated under the names Junco hyemalis Carolinensis and Vireo solitarius alticola, respectively. During the summer of 1887 it was my good fortune to visit this very interesting region, in company with Mr. Henry Gannett, Chief Geographer of the U. S. Geological Survey. By Mr. Gannett's kindness I was enabled to accompany him during a buckboard drive of several hundred miles through the Great Smoky Mountains of Tennessee and North Carolina. Although we entered the mountains in the last week of July, migration had already begun, and it was impossible in most cases to discriminate between the resident and migrant birds. In the case of the Junco, however, young were found in all stages of development from the newly hatched nestling to the fully adult bird; and the important fact was ascertained that the local form inhabiting these mountains is specifically distinct from its northern congener. Hence it must stand as Junco Carolinensis Brewster. Of mammals, the Black Bear, Wolf, Deer, Wild Cat, both Red and Gray Foxes, Raccoon, Opossum, and Gray Squirrel still occur in greater or less abundance according to the locality and altitude. The Panther, Porcupine, Pekan, and Varying Hare are unknown. The Chipmunk (Tamias striatus) and Woodchuck or Ground Hog (Arctomys monax) were common in places in the Alleghanian belt, about half way up the mountains; and the Gray Rabbit (Lepus sylvaticus), Red Squirrel (Sciurus Hudsonius), and a Red-backed Mouse (Evotomys), were common on the higher summits. The latter The latter genus is circumpolar in distribution and has not been previously recorded from any locality south of Massachusetts The present representative of the genus is about double the size of the Canadian Evotomys Gapperi, and proves to be distinct from any previously described species. It may be characterized as follows: |