April io, 19 13] 



NATURE 



of at least 150 miles in diameter, and were no doubt 

 produced by a huge exploding" fireball. The morning" 

 in question was clear and bright. E. G. Fenton. 

 Rio Gallegos, Patagonia, February 12. 



On the Gain of Definition obtained by Moving a 

 Telescope. 



Is not the case mentioned by M. E. J. Gheury in 

 Nature of March 27 (p. 86) but a special case of the 

 familiar fact that an object which is so like its back- 

 ground as to be invisible when at rest is commonly 

 visible when it moves? In this case, as the telescope 

 moved, the signal in its field of view was to the eye 

 fixed to its evepiece an object moving against the 

 background of misty sky, which it so nearly re- 

 sembled as to be invisible when at rest. Is not the 



NORTHERN METHODS OF BURIAL IN THE 

 IRON AGE. 



MR. SCHETELIG'S excellent memoir 1 

 describes the recent more precise investiga- 

 tions which correct and elucidate older work. 

 Relics other than from graves are insignificant, 

 and the nominal restriction to Yestland scarcely 

 lessens the interest, for local discoveries are 

 throughout compared with those in other provinces 

 and countries. Neither a catalogue raisonnd of 

 antiquities, nor a general account of the evolution 

 of Norwegian culture during the Iron Age, the 

 volume serves as a foundation for works of those 



-The Byrkje grave 



; of the excavation. From " Vestlandske Gn 



fra Je 



explanation as follows? Visibility of the object, and 

 in particular of its outline, depends on contrast be- 

 tween it and its background. There is commonly 

 some contrast, but often so slight as not to attract 

 attention when the object is at rest. When, however, 

 the object moves, the brain receives successive impres- 

 sions of contrast as the image of the object falls 

 on one part of the retina after another. Thus the 

 brain receives a cumulative impression of contrast 

 between the object and the background, and the object 

 becomes "visible." 



If this be not, as perhaps it is not, a perfect ex- 

 planation of this familiar fact, there are probably 

 •manv others beside myself who will be glad to know 

 what the correct explanation is. 



Candahar, Reigate. G. W. Butler. 



NO. 2267, VOL. 91] 



two different classes. The objective account of the 

 graves themselves, and of the disposition therein 

 of the varied remains, is its endeavour; and its 

 general conclusions relate mainly to the develop- 

 ment of burial methods. 



The third and fourth centuries a.d. are, in 

 Vestland as elsewhere, those most influenced by 

 Roman culture, while during the fifth and sixth 

 centuries more original lines were followed. 

 During the third century, however, a greater 

 change occurred than about the year 400 ; it was 



1 " Bergens Museums Slcrifter." Ny Raekke. Bd. ii. No. I. Vest- 

 landske Graver fra lernalderen. By Haakon Schetelig. Pp. iii+242. 

 (Bergen : A/S John Griegs Boktrykkeri, 1,1 ) 



