July 



SCIENCE. 



29 



to the Rocky Mountains, where they found old Ilino. All live 

 'there in the caves of the rocks." 



Models of the Ocean's Bed. 



The Hydrographic Office has sent to the Cincinnati exhibition a 

 collection of charts, photographs, etc., illustrating the work of the 

 office and the modes of doing it. These will be interesting to sci- 

 entific men, teachers and students, but, except the photographs, are 

 not likely to arrest the attention of the average visitor. But there 

 are two plaster-of-Paris models in the collection that are certain to 

 be examined with curiosity, and studied with profit, by every one 

 who stops to look at them. They are models of the bed of the At- 

 lantic Ocean and of that of the Caribbean Sea. These have been 

 made by Mr. E. E. Court, of the Hydrographic Oflice, and the charts 

 from which they were constructed have been carefully revised by 

 ■Commander J. R. Bartlett and Lieut. J. L. Dyer, respectively for- 

 mer and present hydrographer. 



Each of these models shows the contour of the bottom of the 

 sea, that of the Atlantic embracing the whole ocean from latitude 

 60" north to latitude 4.0° south, or from Greenland in the north to 

 the unknown region in the south, and includes the Mediterranean 

 Sea on the east, and the Caribbean Sea and a part of the Gulf of 

 Mexico on the west. The chart from which the necessary data 

 were plotted in order to make the model was compiled on a very 

 large scale from the charts of the United States and all foreign 

 hydrographic offices, the very latest deep-sea soundings having 

 been utilized. The contour-lines are drawn according to these 

 soundings. This chart, while it tells the whole story to the expe- 

 rienced hydrographer, — the figures with which it is covered pos- 

 sibly conveying to his mind a picture of how the bed of the Atlan- 

 tic would look if spread out before him so that he could get a 

 bird's-eye view of it, — is entirely meaningless to the great mass of 

 people. But in the model that is constructed from the chart every 

 •depression of the ocean is represented by a corresponding depres- 

 sion in the plaster-of-Paris ; so that even a child, with a few words 

 of explanation, can obtain from it a clearer, more vivid, and more 

 correct idea of how the bed of the ocean looks than the man of sci- 

 ence could obtain from a chart. 



The horizontal scale of the chart and model is sixty nautical 

 miles, or one degree of longitude, on the equator, to each si.x-tenths 

 of an inch ; and the vertical scale is fifty times as great as the hori- 

 zontal. 



The original model was made of wooden boards, one-eighth of 

 an inch thick, each layer representing 250 fathoms of actual depth 

 of the sea. The intermediate soundings are also very carefully 

 represented by carvings of the boards. When the entire contour 

 had been fully represented in the wooden model, a plaster-of-Paris 

 cast was made from it, and this was carefully painted so as to 

 represent in their actual colors, as shown by deep-sea soundings, 

 the mud at the bottom of the sea. As the depth increases each 

 thousand fathoms, the shade becomes darker and darker, the dark- 

 est being in the deepest place known, — 4,561 fathoms, or about 

 5.2 statute miles. 



There are many things shown by this model that will be surpris- 

 ing to almost ever)'body except the expert hydrographer. One of these 

 is the great height of many of the small islands from the ocean's 

 bed, when compared with their area either above the surface of the 

 water or where they rest upon the bottom of the sea. Of course, 

 this height is exaggerated in the model by making the perpendicu- 

 lar scale fifty times as great as the horizontal scale; but, even 

 allowing for that, these islands stand up like tall, narrow, truncated 

 cones, many of them not being more than twice as far across at the 

 base as at the top. 



The model of the bed of the Caribbean Sea was designed by 

 Commander J. R. Bartlett, and the chart was compiled from deep- 

 sea surveys made by himself and by Lieut.-Commanders \V. H. 

 Brownson and Z. L. Tanner. The latest soundings are embodied 

 in it. In this model, of which the horizontal scale is thirty- three 

 miles to an inch and the vertical thirty-three times the horizontal, 

 :the topography of the land is given in the same proportion as the 

 depths of the sea. 



Duplicates, or even photographs, of these models would be of 

 ^'ery great value in the teaching of physical geography. That of 



the bottom of the Atlantic Ocean would give a pupil more actual 

 instruction in a quarter of an hour than a week's study of descrip- 

 tive text. 



ELECTRICAL SCIENCE. 

 Continuous and Alternating Currents. 

 In the last few months discussions have taken place, both in England 

 and this country, as to the relative value of continuous and alternating 

 currents for the distribution of electrical energy. In England the 

 employment of storage-batteries with the continuous current has 

 been advocated : here the simple direct system has been pitied 

 against the alternating. We have noticed these discussions from 

 time to time : now that they are finished, it will be well to sum up 

 the results. 



The alternating system, employing induction-coils or trans- 

 formers, has the advantage of allowing the current to be distrib- 

 uted at a high potential to the ponits of consumption, and there- 

 fore it requires distributing-wires of comparatively small section. 

 There seems little doubt, as matters now stand, that it is best for 

 scattered towns, or even in cities if the lighting is mainly confined 

 to theatres, clubs, stores, etc., which are at a considerable distance 

 apart, and which are to be supplied from a central station. When 

 it comes to domestic lighting, however, where we wish to supply 

 entire districts in cities with electric lights instead of gas, the case 

 is different. Let us consider the availability of the three systems 

 — alternating, direct, and direct with storage — for this purpose. 

 The practice with the alternating system at present is to have a 

 transformer for each house to which lights are supplied. When a 

 large number of houses are to be supplied in a city district, this 

 plan cannot be economically carried out, especially if the wires are 

 forced under ground. The insulation of such a complicated net- 

 work of high-potential wires would be difficult and expensive, — 

 almost impracticable, in fact. Again : as each house would have 

 a transformer whose capacity would be the maximum number of 

 lights that would be used, and as the average number of lights is 

 only a small fraction of the maximum, the transformers — which 

 are not economical when their load is small — would have a low 

 average efficiency. If the alternating system is to be introduced 

 into cities to seriously displace gas, it must be on some such plan 

 as Mr. Kapp proposes. Large converters are placed at different 

 points in the district to be lighted, and the current is distributed at 

 low potential from these. It will be found, if this is done, that the 

 saving in wire is not so large as might be expected, for the greatest 

 expense will be in the low-potential distributing-mains. 



The only storage-battery system in extended practical use is that 

 employed by Mr. Crompton. A number of sets of cells are dis- 

 tributed in sub-stations through the district to be lighted, the dif- 

 ferent sets are connected in series, and the lamp-circuits are taken 

 from the terminals of each set of cells. The batteries act then 

 partly as a converter, allowing high-tension currents for distribu- 

 tion, with a comparatively small difference of potential at points of 

 consumption. Another advantage lies in the fact that the cells can 

 be charged when the demand is light, and discharged at the time 

 of maximum demand, thus allowing a smaller generating-plant. 

 Mr. Crompton claims a high efficiency for the arrangement, and he 

 is no doubt right. There is a loss, of course, in the part of the 

 energy stored, but very little in that converted ; and, as the former 

 is not a large part of the total output, an efficiency of eighty-five 

 per cent is not improbable. Mr. Crompton also claims that the 

 repairs of the battery will not amount to more than ten per cent of 

 their cost. The disadvantage of this system lies in the fact, that, 

 with batteries in the circuit, insulation is difficult; and while the 

 difference of potential between the leads taken from the two ends 

 of a set of cells is only, say, one hundred volts, yet the difference of 

 potential between these and the ground depends on the position 

 of the set, and might be high. In fact, we have the disadvantage 

 of distributing at a comparatively high absolute potential, with all 

 the ditTiculty of insulation that it entails. 



The simple direct system has the advantages of a high efficiency 

 and simplicity, and it is economical within a limited area of distribu- 

 tion. It has the disadvantages that the station must be located 

 near the centre of the district to be illuminated, and the area of 

 operation is restricted. 



