March 30, 19 16] 



NATURE 



lOI 



kinds of glass in the construction of telescope objectives 

 and microscope objectives. 



■■ Regarding the latter aim, a series of objectives 

 adjusted for the short continental tube is nearly 

 finished ; another series for your English microscopes 

 — which requires different formulas — has been begun; 



and you and Mr. have at hand the first specimens 



of that series. 



"The optical features of the new constructions, which 

 are represented by this i/8th of 1-4 ap., may be de- 

 -"- ! in that way; the various corrections are of a 

 r order than could be obtained formerly (or, more 

 -wL^Liy spoken, the residuals of the various corrections. 

 I.e. the defects of collection of the rays, are of a higher 

 order according to mathematical terminology, (i) With 

 the old kinds of crown and fiint glass two different 

 colours only could be collected to one focus, a secondary- 

 spectre remaining uncorrected. With the new glass 

 those different colours unite at one point, a 

 tertiar;- deviation being left only. (2) Formerly 

 the spherical correction was confined to the rays of 

 one colour; this correction being made for the middle 

 part of the spectrum, the systems remained under- 

 corrected, spherically, for the red rays, and over- 

 corrected for the blue rays. Now the correction ol 

 sph. aberr. is obtained for two different rays of the 

 spectrum at the same tim.e, and the objective shows the 

 same degree of chromatical correction for the central 

 as for the marginal part of the aperture. (Of course, 

 this higher degree of correction is not given by the 

 glass from itself — it requires a ver\^ careful utilisation 

 of the optical properties of the various kinds of glass 

 at disposal, in order to fulfil all those conditions, and 

 this was not even possible except by means of a greater 

 cornplication of the constructions ; I was obliged to 

 introduce five separate lenses (for the aperture 1-4) 

 instead of the four applied hitherto). 



" The objective at hand is constructed on the single- 

 front-type. It contains ten single lenses in five separate 

 parts. Two only of these ten lenses contain silicious 

 acid ; the glasses of the other eight are phosphates ana 

 borates — the Crown and Flint glass which has been 

 used by the opticians hitherto, does not contain, as 

 essential constituents, more than six chemical elements, 

 O, Si, K, Na, Ca, Pb; the lenses of the i/8th contain, 

 as essential components of the glass, not less than 

 fourteen elements." 



" I did not introduce a greater aperture than 1-40 in 

 order to preserve a convenient working distance — 

 which, in fact, is =025 mm. = 1/100 in. The two 

 oculars sent with the objective are constructed with 

 the aim to compensate certain aberrations outside the 

 axis, which cannot be got rid of in the objectives (of 

 wide aperture). The whole series of objectives, high 

 and low powers, shall be so arranged, that this com- 

 pensation is always obtained bv the same series of 

 oculars." 



This last letter, I think, will be acepted as setting out 

 mter alia, in a remarkably lucid wav the optical advan- 

 tages obtained by the introduction and employment of 

 the Jena glass in optical constructions. 



F. J. CHESmRE. 



Hamilton and the "Quantification of the Predicate." 



vrl^^^'f ^'w^T.^°r ^^^''^^ -3. P- 78, in a review of De 

 >lorgan s Budget of Paradoxes," re-issued by the 

 ^fw-n?"''^ Publishing Co., there is an allusion to 

 tifi.o^^ ^^"^ Hamilton's "famous theorv of the quan- 

 tification of the predicate." ^ 



nen£L*^f°7 ^^^ ^^^^ ^* °"t ^^ George Bentham, a 

 HnSTf T ^^'"i^y Bentham, in 1827, "in his " Out- 

 Iftur^fc p ■^''''- ^^J^ew«d by Hamilton in the Edin- 

 \^utgh Review in 1833, and again raised bv Mr. War- 



NO. 2422, VOL. 97] 



low in the Athenaeum at the end of 1850, as may be 

 read in the Contemporary Review, May, 1873, pp. 

 82 1-24. 



Although Bentham never pushed his theory, it is 

 clear that it came into Hamilton's mind from 

 Bentham 's book, and, as so often happens, the actual 

 originator has been overlooked. B. D. J. 



THE ARCHAEOLOGICAL SURVEY OF 

 NUBIAA 



I N the accounts of the preceding reports which 

 •'- have been published in Nature attention has 

 been directed to the exceptional thoroughness of 

 the work, both of excavation and surveying, and 

 the completeness of the presentment of the new 

 information brought to light in this important 

 archaeological survey, which has been carried out 

 by the Egyptian Survey Department. 



In the present report Mr. Firth has fully main- 

 tained the high standard of excellence; and the 

 complete and lucid statement of the facts, the 

 liberal supply of text-figures, and especially the 

 admirable collotypes, enable the reader almost to 

 see and fully to understand the whole of the work, 

 without the discomfort of living in a Nubian 

 camp. 



It is a matter for congratulation that this impor- 

 tant and difficult investigation was carried out 

 with such insight and thoroughness, for the flood- 

 ing of the country makes it impossible ever to 

 survey Lower Nubia again for archaeological in- 

 formation. Without the knowledge so acquired 

 the door would have been shut for ever upon a 

 proper understanding of the early history of the 

 Sudan, which is now being revealed by Prof. 

 Reisner's excavations in the Kerma basin. More- 

 over, many of the difficulties in interpreting the 

 story of Egypt would have been quite insurmount- 

 able without this information to make clear what 

 was happening south of the First Cataract. 



Most of the volume is devoted to the primary 

 object of such a report, viz., the detailed and im- 

 partial statement of all the facts brought to light. 

 It includes a brief account of the town site of 

 Pselchis, and a full account of the mode of con- 

 struction and contents of every grave. 



The special importance of this report, however, 

 depends upon the fact that it deals so largely 

 with the remains of the distinctively Nubian cul- 

 ture, of which, from the circumstances of the 

 case, it must represent for all time the chief source 

 of information. In the introductory twenty-four 

 pages Mr. Firth gives a well-balanced and illu- 

 minating survey of the early movements of people 

 in the Nile valley, in which he clearly defines the 

 position and the distinctive cultural relations of 

 the Middle Nubian people (the " C-group "), The 

 only criticism that I have to make of his account 

 of this interesting people is the wholly unwarrant- 

 able suggestion of "the possibility that the C- 

 group represents an immigration from the south- 

 west of a mixed Negro and Libyan stock from 



^ "The Archseological Survey of Nnbia." Report for 1909-10. By CM. 

 Firth. (Cairo: Goremment Press, 1913.) Price L.E. 2. 



