vii 



Aided by his remarkable facility in calculation (for fonr-figure logarithms 

 he scarcely required the aid of the tables), he in 1853, conjointly with 

 Olufsen and with pecuniary assistance from Denmark, at the request of 

 the Society of Sciences at Copenhagen, completed his solar tables ; and 

 likewise in 1857 the lunar tables printed by the English Admiralty, for 

 which the Parliament of Grreat Britain voted him the sum of ^1000. 



In 1838 he published the theory of the moon's motion in a special 

 work, ' Pundamenta nova investigationis orbitse verse quam Luna per- 

 lustrat the exposition of the theoretical calculation of the perturba- 

 tions employed in the lunar tables appeared in 1862-64, in two elaborate 

 treatises published in the Transactions of the Eoyal Society of Sciences in 

 Saxony. An appendix treats of the verification of chronological eclipses. 

 He wrote a series of treatises on the theory of the absolute Perturbations 

 of the Asteroids, to which he appended tables of Egeria. 



The comet disturbances he treated in two special works — the one 

 entitled " Ermittelung der absoluten Storungen in EUipsen von beliebiger 

 Excentricitat und Neigung," 1843 (which was translated into Erench by 

 Mauvais) ; the other a prize treatise of the Erench Academy, ' Memoire 

 sur le calcul des Perturbations qu'eprouvent les cometes.' As examples, 

 he gives the disturbances of Encke's comet by the Earth and Saturn. 



Eor his ' Untersuchungen iiber die gegenseitigen Storungen des 

 Jupiters und Saturns ' he had received in 1830 the prize offered by the 

 Berlin Academy. A farther posthumous memoir, "Ueber die Storungen 

 der grossen Planeten, insbesondere des Jupiters," has just been pubhshed 

 in the Transactions of the Saxon Society. In the same Transactions he 

 published, amongst other things, very elaborate memoirs on the "Theorie 

 des Aequatoreals " (1855), on " Theorie der Sonnenfinsternisse und ver- 

 wandten Erscheinungen " (1858), on the " Bestimmung der Sonnen- 

 parallaxe durch Yenusvoriibergange vor der Sonnenscheibe " (1870), in 

 relation to the Transit of 1874, two memoirs connected with dioptrical 

 researches (1871 and 1874), besides a long series of memoirs on the 

 Calculus of Probabilities and the higher Geodesy (1865-1869), to which 

 he was led by his taking part in the European measurement of an arc of 

 a meridian. 



One of his latest memoirs treats of the determination of errors in the 

 division of a graduated rectilinear scale, and was written with a view to 

 the expected photographic measures of the Transit of Venus. 



Among the memoirs of the London Astronomical Society we may 

 mention two important papers on the Inequalities of long period in the 

 Moon's motion (1847), and on the Eigure of the Moon (1854). In the 

 former he examines the influence of Yenus on the mean longitude of the 

 moon, and in the latter he endeavours to show that the centre of the figure 

 of the moon does not coincide with her centre of gravity, but that the 

 latter is about 59 kilometres further from us than the former. 



After the death of Schumacher, Hansen shared for some time the 

 editorship of the ' Astronomische Nachrichten ' which Schumacher had 



