108 



SCIENCE. 



[N. S. Vol. II. No. 30. 



the weather, etc., are treated pleasant! j^ in 

 various chapters ; but the chief results of 

 the International Circum-polar Stations are 

 hardly alluded to. In the chapter on the- 

 ories respecting the origin of the aurora no 

 mention can be found of Lockj'er's ingenious 

 meteoric theorj^. The data given respecting 

 the height of the aurora are likewise far 

 fi'om complete; and in the table on page 71, 

 gi^dng wave-lengths of lines found in the 

 auroral spectrum, only 14 lines are given, 

 which doubtless was the full number in 1882, 

 but which now contrasts strangely with 

 Gyllenskiold's detailed descrijrtion of 32 

 lines. 



Lemstrom's experiments upon the artifi- 

 cial reproduction of the aurora do not seem 

 to our author to be all that has been claimed 

 for them; and, after noticing Tromholt's 

 unsuccessful attempt with similar apparatus, 

 he gives the experience of M. Vaussenat at 

 the Pic du Midi, who, at an elevation of 

 2,877 metres, with a network of wire cover- 

 ing an area of 640 square metres, obtained 

 nothing in the way of an artificial aurora. 

 So, like many another explanation of the 

 aurora, this may be laid away for the pres- 

 ent as unproven. The true relation of the 

 aurora to magnetic perturbations still re- 

 mains to be determined. Angot repeats a 

 suggestion which has been made elsewhere, 

 viz. : that many of the difficulties which 

 now present themselves in connection with 

 auroras and magnetic perturbations will 

 disappear if it be understood that, under the 

 one name of aurora, we are now classifying 

 phenomena which may be of verj' different 

 natures. Let us make one class of auroras 

 embrace those widelj' extended magnificent 

 displays which are accompanied with mag- 

 netic disturbances, and another class those 

 displays w^hich are local in character and 

 more in the nature of manifestations of at- 

 mospheric electricity. 



There remains little to be said about the 

 relation of sun-spots and auroras, other than 



that the agreements thus far made out are, 

 it is to be feared, more apparent than real. 

 We seem, indeed, to be but little removed 

 from the military authorities who, at Copen- 

 hagen in 1709, during a verj'' brilliant 

 aurora, ordered that the troops be paraded, 

 the drums beaten and arms presented. We 

 are able to do as little. A. M. 



Geological Survey of Michigan. L. L. Hub- 

 bard, State Geologist. Vol. v., 1881- 

 1893. Part I. Upper Peninsula, 1881- 

 1884. Iron and Copper Eegions, by Carl 

 Eominger, pp. 179, 3 plates and a map. 

 Part II. Geology of Lower Michigan, 

 vdth. reference to deep borings. C. E. 

 Wright and A. C. Lane, with an intro- 

 duction by L. L. Hubbard, pp. 100, 

 plates LXXIII. and a map. Lansing, 

 1895. 



The Geological Survey of Michigan is to 

 be congratulated on finally possessing, as we 

 learn fi-om this report, a house of its own, 

 where its collections can be permanently 

 stored and kept together for reference. 

 There is so much complexity in the geology 

 of the Upper Peninsula, and so miich im- 

 portance attaches to the determination of 

 obscure species of rocks, that a permanent 

 home is indispensable, and the sole regret 

 is that it was not earlier attained. The 

 volume before us resumes, in the same style, 

 the series of Michigan reports that tempo- 

 rarily ceased with the issue of Vol. IV., in 

 1882. Pai-t I. consists of a manuscript of 

 Dr. Carl Rominger, formerly State Geolo- 

 gist, that was prepared about 1882, and has 

 remained unpublished to date. To properly 

 appreciate Dr. Eominger's paper on the 

 iron districts one must place one's point of 

 view back in 1883 and efiace fi-om mind as 

 far as possible the work of Irving, Van 

 Hise and G. H. Williams, the reports of 

 Wads worth, the reviews of Alex. Winchell 

 and many other minor papers on the petro- 

 graphy and stratigraphy of this difficult 



