316 



SCIENCE 



[N. S. Vol. XLIII. No. 1105 



POLARIZATION OF GLOBIGERINA 



On examining a group of ancient micro- 

 scopic slides of modern foraminifers it was 

 found that they polarize very beautifully, 

 showing with plane polarized light several 

 concentric circular spectra and a very clear 

 black cross with broad bands and a broadened 

 central area. This appeared most perfectly 

 with globigerina, the young forms with but a 

 single globe showing most perfectly. In the 

 larger forms each half enveloping globe shows 

 the same phenomena very clearly. The spec- 

 tral rings are crowded toward the edge of the 

 sphere and the explanation is clearly that the 

 hollow sphere is in effect a circular wedge with 

 its thinnest part at the center and becoming 

 thicker radially, at first gradually and at last 

 much more rapidly. 



It was found also that minute valves of a 

 bivalve, in shape like a quahog, would do 

 exactly the same things only the rings were 

 pear-shaped with a projection at the beak of 

 the shell and broader and brighter. It was 

 clear that the very sharp black cross was due 

 to the fact that the outer layer of the shell is 

 fibrous and we may deduce that the similar 

 black cross in the globigerina is due to a 

 minute fibrous structure in the shell of the 

 latter. 



Thin plates of the inner mother of pearl 

 layer of Margaritifera and Pinna polarize 

 brilliantly and give the lemniscate of a nega- 

 tive biaxial mineral with the axis at right 

 angles to the layers, and so the mineral in all 

 these cases is doubtless aragonite. 



The smaller species of deep sea Globigerina 

 show all this most beautifully and are a con- 

 venient object to demonstrate the stationary 

 black cross and the higher order spectra in 

 concentric rings. The silicious forms, 

 Diatoms, Polycistina and sponge spicules do 

 not polarize. This is true of the marine 

 sponges like Aspergillum and Euplectella, but 

 the freshwater sponge Grantia from the ponds 

 around Amherst polarizes very strongly. 



B. K. Emerson 



Amhekst, Mass. 



the teaching of the history of science 

 To THE Editor of Science : In his interest- 

 ing and valuable paper on " The Teaching of 



the History of Science" published in Sci- 

 ence, November 26, 1915, Mr. Brasch calls at- 

 tention to early courses in this subject which 

 were given at the Massachusetts Institute of 

 Technology, referring particularly as one of 

 these to a reading course on the history of the 

 physical sciences laid out as a requisite for 

 graduation in the course in physics. The date 

 which he mentions for its institution is 1887. 



In fact, however, its beginning was much 

 earlier. The writer from the outset of his work 

 as a teacher had recognized the surprising lack 

 of perspective existing among college students, 

 but chiefly on account of the great pressure 

 upon the teaching staff which existed here as 

 everywhere, it was not possible at the time 

 to institute a course of oral lectures upon the 

 subject and the best that could be done was to 

 lay out a suitable course of required reading, 

 which was necessarily limited to physical sci- 

 ence. This reading course was established at 

 a considerably earlier date than that men- 

 tioned by Mr. Brasch, and is found set forth 

 in the Catalogue of the Institute for 1880-81 

 in the scheme of studies leading to a degree in 

 physics. A required reading course upon the 

 logic of scientific investigation is also referred 

 to in the same scheme. 



A similar course on the history of the nat- 

 ural sciences is referred to in the same cata- 

 logue of the Institute in the scheme of the 

 coiu-se in natural history. 



C. R. Cross 



SCIENTIFIC BOOKS 



British Ants, Their Life-TIistory and Classi- 

 fication. By H. St. J. K. Donisthorpe. 

 Plymouth : Wm. Brendon & Son, Ltd., 1915. 

 Pp. XV-}- 373, 18 pis. and 93 text-figs. 

 In this attractive volume we are given for 

 the first time an exhaustive monograph of the 

 ant-fauna of Great Britain, the result of 

 many years of patient labor by one who served 

 his biological apprenticeship as an ardent stu- 

 dent of myrmecophiles. The volume serves 

 also as a useful manual for the study of ants 

 in general since it contains concise chapters 

 on the anatomy, development and behavior of 

 ants and the methods of keeping and studying- 



