672 HENRY SOTHERAN & CO., 140, STRAND, W.C., AND 43, PICCADILLY, W. 



13436 PLtJCKER (Julius; Univ. Bonn; F.R.S.) COMMENTATIO de CRYSTALLORUM et GAZORUM 

 CONDITIONE MAGNETICA, qualis hodie intelligitur, 4to. (pp. 34), sewn (scarce), 6s Qd Eonnce [1854} 



'Pliicker discovered that a piece of tourmaline, which is itself feebly paramagnetic, behaved as a diamagnetic body 

 when so hung that the axis of the crystal was horizontal. Faraday, repeating the experiment with a crystal of bismuth, 

 found that it tended to point with its axis of crystallization along the lines of the field axially. The magnetic forces 

 acting thus on crystals by virtue of their possessing a certain structure he named magne-crystallic force. Pliicker 

 endeavoured to connect the magne-crystallic behaviour of crystals with their optical behaviour, giving the following law ' 

 etc. etc. Prof. Silvan us Thompson, F.R.S. 



13437 NEUE GEOMETRIE des RAUMES gegriindet auf die Betrachtung der geraden Linie als 



Raumelement, mit Vorwort von A. CLEBSCH [herausgegeben von FELIX KLEIN] ; with diagrams, 

 2 parts 4to. sewn, Qs (p. M. 15) Leipzig, 1868-9 



13438 SYSTEM der ANALYTISCHEN GEOMETRIE, auf neue Betrachtungsweisen gegriindet, und 



insbesondere eine ausfiihrliche THEORIE der CURVEN DRITTER ORDNUNG enthaltend ; with 6 

 plates, Berlin, '35 : THEORIE der ALGEBRAISCHEN CURVEN, gegriindet auf eine neue Behandlungs- 

 weise der analytischen Geometric ; with plate, Bonn, '39 : SYSTEM der GEOMETRIE des RAUMES, 



' The System der analytischen Geometrie, 1835, contains a complete classification of plane curves of the third order, based 

 on th; nature of the points of infinity. The Theorie der algebraischen Curven, 1839, contains, besides an enumeration of 

 curves of the fourth order, the analytic relations between the ordinary singularities of plane curves known as l Pliicker 's 

 equations ', by which he was able to explain ' Poncelet's paradox '. The discovery of these relations is, says Cayley, ' the 

 most important one beyond all comparison in the whole subject of modern geometry.' By considering space [in Geamnt,-i< 

 des Raiimes] as made up of lines he created 'a new geometry of space'. Regarding a right line as a curve involving four 

 arbitrary parameters, one has the whole system of lines in space. By connecting them by a single relation, he got a 

 ' complex ' of lines ; by connecting them with a twofold relation, a ' congruency ' of lines '.Prof. Cajori. 



J3439 , und Johann Wilhelm HITTORF, Univ. Munster: On the SPECTRA of IGNITED 



GASES and VAPOURS, with especial Regard to the different Spectra of the same Elementary Gaseous 

 Substance, with 3 folding plates of spectra (one coloured), 4to. (pp. 29), sewn (scarce), 6s Qd 1864 

 'As early as 1862, Pliicker pointed out that the same substance may give different spectra at different temperatures. 

 He and Hittorf found for hydrogen, nitrogen, and sulphur fumes two kinds of spectra, namely a weak band spectrum and 

 a bright line spectrum.' Prof. Cajori. 



13440 , NOTICE sur les TRAVAUX de [avec Bibliographic (pp. 5)] , par ALFRED CLEBSCH, traduit 



par PAUL MANSION, 4to. (pp. 30), sewn, 2s Roma, 1872 



13441 PLTJMMEB (Henry Crozier ; Royal Astronomer of Ireland) A METHOD of MECHANICALLY 

 COMPENSATING the ROTATION of the FIELD of a SlDEROSTAT, with 3 diagrams, 8vo. (pp. 6), sewn, 

 Is 1901 



13442 THE SAME; with NOTE on the GEOMETRY of the SIDEROSTAT, with 2 diagrams, 8vo. 



(pp. 10), sewn, \s Qd 1901 



13443 On a METHOD of REDUCING OCCULT ATIONS of STARS by the MOON, with the Reduction 



of Occupations observed on three Occasions at the Liverpool Observatory, 8vo. (pp. 12), sewn, IsQd 1901 



13444 NOTE on the GEOMETRY of the SIDEROSTAT, with 2 diagrams, 8vo. (pp. 4), sewn, Is 1901 



13445 NOTE on MR. BRYAN COOKSON'S PAPER, 'On the ACCURACY of EYE OBSERVATIONS of 



METEORS, and the DETERMINATION of their RADIANT POINTS ', 8vo. (pp. 8), sewn, Is 1901 



13146 PLUMMER (William Edward, F.R.A.S., Director of Liverpool Observatory) On the ORBIT of 

 DENNING'S COMET (1881 V.), 4to. (pp. 15), sewn, Is Qd ' [Dublin, 1883] 



13447 PRELIMINARY NOTE on the POSITION of the LIVERPOOL OBSERVATORY ; OBSERVATIONS 



of COMET II. 1894 (GALE), 8vo. (pp. 13), sewn, Is Qd 1894 



13448 POEY (Andres) ETOILES FILANTES observers a la Havane du 24 Juillet an 12 Aout, et 

 Remarques sur le Retour Periodique du Mois d'Aout, 4to. (pp. 5), sewn, Is Qd 18<>4 



13449 POGGENDORFF (Johann Christian ; Univ. Berlin ; founder of < Annalen der Physik und 

 Chemie ') GESCHICHTE der PHYSIK : Vorlesungen an der Universitiit zu Berlin [herausgegeben 

 von W. BARENTIN] ; with 40 woodcuts, thick 8vo. new hf. calf gilt, uncut, t. e. g. (scarce), 18s Qd 



Leipzig, 1879 

 Still one of the best works on the history of physics. 



13450 METHODS zur QUANTITATIVEN BESTIMMUNG der ELEKTROMOTORISCHEN KRAFT IN- 



CONSTANTER GALVANISCHER KETTEN ; with 2 diagrams, 8vo. (pp. 31), seven, with author's inscr. 

 to E. Solly, F.R.S. (scarce), Qs Qd [ibidem,] 1841 



In this tract the author first published his famous method of compensation for comparing the electromotive force of 

 various galvanic cells. 



' Die Poggendorff sche Methode ist bis auf den heutigen Tag in ihreu verschiedenen Modifikationen die beste, um nicht 

 zu sagen die einzige, welche fur inkonstante Kritfte angewendet werden darf.' Hopped Gtsch.d. Elektnzitiit. 



13451 POGSON (Norman Robert, F.R.A.S., Govt. Astronomer, Madras) TELEGRAPHIC DETERMIN- 

 ATIONS of the DIFFERENCE of LONGITUDE between Karachi, Avanashi, Roorkee, Pondicherry, 

 Colombo. Jaffna, Muddapur and Singapore, and the Government Observatory, Madras, 4to. 

 cl., 5* Madras, 1884 



This work was privately printed, and copies were presented by order of the Governor in Council at Madras. 

 v. Nos. 11268-71, ante. 



13452 POHL (Georg Friedrich; Univ. Breslau) Der ELEKTROMAGNETISMUS, theoretisch-praktisch 

 dargestellt, ERSTE ABTHEILUNG (sovveit erschienen) ; withholding plates, 8vo. sewn, 5s Berlin, 1830 



The author proposed a new theory of the galvanic current, based on that of galvanic and chemical action being 

 identical. He was the inventor of the current reverser (Pohl's gyrotrope). 



13453 POHL (Joseph Johann) Ueber die SIEDEPUNCTE mehrerer ALHOHOLHALTIGER FLUSSIG- 

 KEITEN und die darauf gegriindeten Verfahren den Alkoholgehalt derselben zu chemisch- 

 technisehen Zv._ecken zu bestimmen ; with plate, folio, sewn, 5s Wien, 1850 



13454 POINCARE (Lucien, Inspecteur -General de V Instruction publique) ELECTRICITY : Present and 

 Future, translated by JASPER KEMMIS, 8vo. cl., Is Qd (Is Qd nett) [1908] 



