XIX 



impossible, owing to the want of a suitable observatory in Upsala, to make 

 really accurate observations there. 



Angstrom's published w^orks on astronomy are not numerous. The 

 most important among them are that entitled ' Ad theoriam Cometarum 

 additamenta ' (which he published as an evidence of his competency for 

 the post of Assistant Professor), and another, first published, in 1862, in 

 the ' Transactions ' of the Society of Sciences of Upsala. 



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This latter memoir illustrates Angstrom's power of arriving at his end 

 by a more direct process, but which others could only attain by long cal- 

 culation. Both papers show considerable originahty of thought. Thus, 

 for instance, he never approved of the explanation generally adopted of 

 the retardation of Encke's comet by the resistance of the cosmic ether ; but 

 his opinion was that it depended on the perturbations of the little planets 

 situated between Mars and J upiter. There is a note of his on this subject 

 in the ' Comptes Eendus ' of the Academy of Sciences of Stockholm for 

 the year 1854. He considered that, as a rule, modern astronomers collect 

 too many observations, gaining from them very few new results in com- 

 parison to the number and to the immense amount of labour expended. 



The observations on the phenomena of magnetism set on foot by Gauss 

 were originally considered as belonging to the domain of astronomy, an 

 opinion still held by some persons. Gustave Svanberg had, as early as 

 1836, estabhshed at Upsala magnetometers w^hich he had procured from 



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Gottingen. Angstrom became much interested in the observations made 

 with the aid of these instruments after his engagement at the Observatory ; 

 and in the course of a tour abroad, which he made in 1843, he visited the 

 Observatory of Bogenhausen, near Munich, in order to study the new 

 magnetic apparatus which Lamont had constructed. It was more parti- 



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cularly the apparatus to be employed in travelling w^hich attracted Ang- 

 strom's attention. He obtained at Munich some of these instruments, 

 and used them assiduously during the remainder of his journey, making 

 magnetic observations at Gottingen, Paris, Brussels, and other places. 

 Between the years 1850 and 1870 he made a large number of obser- 

 vations on magnetic intensity and inclination in different parts of Sweden, 

 but they were never published. 



Angstrom was commissioned by the Academy of Sciences of Stock- 

 holm to work out the magnetic observations which had been made be- 

 tween the years 1851 and 1853, during the voyage round the world of 

 the Swedish frigate ' Eugenie.' The observer, M. Johannson, had died 



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shortly after the return of that expedition, and Angstrom was considered 

 to be the person most competent for calculating out these observations, 

 because the English instruments employed by M. Johannson were very 



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similar to those which Angstrom was then using for his own obser 

 vations. 



The determinations of constants were executed between the years 



d2 



