December 30, 1892.] 



SCIENCE. 



375 



netic instruments through the day. This great magnetic storm 

 exhibited, if I am not mistakea, its plienomena in the southern, 

 in the northern, in t'e eastern, as well as in the western, 

 liemispheres. I watched the display for most of the two nights 

 at West SpringBeld, Mass., and read many notices of it in the 

 public prints. 



I will add that at 10.45 p.m , Dec. 5, 1893. I saw, to me. an 

 unique phenomenon. The moon was shining brightly, %vhen di- 

 verging bands from the horizon in the north-north west spread at 

 the zenith 60" wide and converged again at the horizon in the 

 south-south-east. They were like thin clouds, through which 

 the stars were easily seen. The belt of Orion was exactly then in 

 their midst I can hken thpir shapes to nothing more than the 

 vibrations of a cord, stretched from horizon, over the zenith, to 

 horizoD again. But they were stationary, and had so far disap- 

 peared at 11.30 P.M., standard time, that only curious traces and 

 patches remained. I fancy that had not the moon been shioing, 

 these beautiful bands woud have shown luminosity. 



I judged that the radiating point in the north north-west was a 

 trifle west of the magnetic meridian there; but our western de- 

 clination here is some nine degrees. These were, of course, 

 parallel bands, the diver;rence and convergence points being the 

 eflfect of perspective. James Hyatt. 



Honeymealbrook Station, N.Y., Deo. 19. 



Alleged Extinction of Mulatto. 



A FEW months since an article appeared iu a medical journal 

 affimiing that the pure mulatto colonies of southern Ohio were 

 dying out after the fourth generation. Can any reader point me 

 to the article in question, or to any definite information bearing 

 on the permanence of the mulatto as a species (or variety)? 



Polytechnic Society, LouisvUle, Ky. JaS. LeWIS HOWE. 



BOOK-REVIEWS. 

 Lessons in Elementary Mechanics. By Sir Philip Magnds. New 



York, Longmans, Green. & Co , 1893. 370 p. 12°. 

 Elementary Manual of Applied Mechanics. By Andrew Jamie- 

 son. London, Griffin & Co. 265 p. 13°. $1.25. 



These two little treatises on mechanics illustrate two ve;-y dis- 

 tinct lines of college and school work, and are each characteristic 

 of its class. Sir Philip Magnus has been distinguished for many 

 years for his success as an author in this field, and his '• lessons " 

 have gone to their thirtieth thousand. The method of treatment 

 of the subject is that which has been endorsed hy authority and 

 become "standard." The usual division of the subject into kine- 

 matics and dynamics is observed; and the latter is again subdi- 

 vided, as customary, into kinetics and statics. Motion, as a more 

 elementary idea than force, is first discussed, then follows the 

 study of force and its effects in the production of equilibrium. 

 The study of kinetics and of statics brings out the diflferences in 

 effect when the body is free to move and when the forces produce 

 no motion. The special feature of the book is the admirable 

 manner in which energy is discussed and its operation illustrated. 

 The extent of the work is such as is expected to suit the wants of 

 the scholar of the first year, and is well adapted to the needs of 

 those proposing to take the London LTni versify couise or other 

 of similar character. For this counlry it will make an excellent 

 high-school course. 



Professor Jamieson's work is characterized by its constant utili- 

 zation of the principles taught, by application in the problems of 

 every-day life and of constructive work. Even its illustrations 

 have the advantage of being selected from among those of builders 

 of machinery illustrating the principles treated. It is intended to 

 meet the needs of students preparing for science and art examina- 

 tions; but should be found of special value to those proposing to 

 enter upon a course of technical education. It would be an ad- 

 mirable work for the better class of manual training schools. 

 from which students pass into the technical colleges and pro- 

 fe.ssional schools of engineering. This establishment of a close 

 relation between the principles taught and their useful applica- 

 tions in industry, and in the design and construction of machines, 



is a matter in which the older text-books have utterly failed, but 

 in which the author uniting a knowledge of principles with 

 familiarity with practice may always succeed, and vpith great ad- 

 vantage to himself in competition with the teachers of the ab- 

 stractions alone. Even the average practitioner would be none 

 the worse for a careful review of this little primer of mechanics. 



The best of books have their little defects; and we observe, in 

 both these piimers of mechanics, the old, and long-ago exploded, 

 ideas on friction; no distinction being made between the laws of 

 solid and those of fluid friction and the "mediate" friction of 

 lubricated surface^. Here are the old laws and the actual fact in 

 " parallel column '" : — 



Lrius of Friction. 



Solid (Jamieson 

 and others). Fluid. Mediate. 



(1) i^ varies as i^ is constant with F varies as / (P) . 



Pressure. Pvar.ving. 



(2) P independent P varies as .4. F varies as/ (4). 



of Areas. 



(3) F independent F varies as F-. F varies as/ (V). 



of Velocity. 



The first of these sets of '• laws" is that usually found unquali- 

 fied in elementary text-books and is. obviously, entirely mislead- 

 ing; although defective lubrication is so common in machinery 

 that the result is less serious than might otherwise be the fact. 



ffgodes!/ (Riverside Science Seiies). By J. Howard Goee. Bos- 

 ton, Houghton, Mifflin & Co. 318 p. 16*. $1.35. 

 Introduction to Geodetic Surveying. By Mansfield Mereiman. 

 New York, J Wiley & Sons. 170p. 8°. 



The first of these books is an historical account of the science 

 of geodesy from the time of the ancients to the present, written 

 in popular and interesting style, and is likely to prove most ac- 

 ceptah e lo the average reader, not an expert, who may desire to 

 know something of the methods which have been adopted in the 

 determination of the dimensions of the ear.h and their results. 

 Its author has enjoyed the rari' privilege of working from the 

 original documents, as he states m his pi'eface, and his sketch 

 thus comes as authoritative. He commences his task by refer- 

 ence to. and brief descriptions of, the primitive notions of the 

 older peoples, and their rude attempts to measure the earth. 

 When their comparative ignorance of the subject, and their lack 

 of insttviments of exact measurement are considered, their 

 approximations to the actual value of these dimensions seem little 

 less than maivellous. The Chaldeans not only knew the earth to 

 be •' round " but made the degree equal to 4,000 steps of a camel, 

 and the circumference of the earth about 24,000 miles. The 

 Greeks and Romans took this quantity to be 250,000 stadia ; the 

 Arabians found it to be between 56 and 57 miles, 71 of our miles, 

 per degree. Feme!, a French geometer of about 1550, measured 

 the degree, and made it about 69 miles. Snell, in 1615, made 

 the first scientific measurement of importance, however, making 

 the arc of a meridian 55,073 toises, which is about 2,000 toises 

 short. The toise is 6.4 feet. 



Picard, in 1670, made the degree 57,060 toises, and so nearly cor- 

 rectly as to give to Newton his famous proof cf the extension of 

 the gravitation of the earth to its satellite. Later work is fa- 

 miliar to all interested in the subject, and it is a pleasure to note 

 that the U. S. Coast Survey has done its share. It is considered 

 by Professor Gore that the computations of Professor Harkness, 

 making the ellipticity of the earth 1:300.2, and tlie quadrant to 

 measure 10,001,816 meters, will prove most exact, although those 

 of Bessel and Clarke are now generally received. 



Professor Merriman's work is a formal and scientific treatise on 

 the work of geodetic surveying. It includes a number of lectures 

 on the figure of the earth, prepared as introductory, and also a 

 discussion of the '• Method of Least Squares." written especially 

 for surveyors and engineers, as well as for students. The third 

 and concluding part contains a synopsis of the methods and com- 

 putations of precise triangulation. The introductory portion 

 gives a history of the development of modern methods and some 

 interesting facts relative to the work of the older geometers and 



