1891-92.] An Error of Instinct. 3 7 



Telescopes.' He then pointed out the method of measuring 

 these, and of ascertaining the focal length of compound sys- 

 tems, such as a microsocope eyepiece, by means of an empiri- 

 cal formula devised by Mr Charles Cross, and fully described 

 by Colonel Dr Woodward in his paper " On the Nomenclature 

 of Achromatic Objectives," in the ' American Science Beview ' 

 for 1872. The formula was — 



m x I 



— where I is the distance between the scale to be magnified 

 and the screen upon which its image is projected by the lens, 

 and m the magnifying power at that distance. 



At this meeting Mr Eobert Stewart, S.S.C., read a paper 

 entitled "Ancient Natural History Beliefs." The paper treated 

 of the scientific notions of some eminent naturalists of a bygone 

 time, and was of a very racy and interesting character. 



IX.— AN ERROR OF INSTINCT. 

 By Mr SOMMEEVILLE GRIEVE. 



(Read March 23, 1892.) 



We have so many wonderful manifestations around us of the 

 unerring instinct of the animal creation, that we are apt to 

 give way to astonishment when it apparently fails. Instinct 

 is seldom wrong, when guided by its own promptings amid 

 natural phenomena ; but when brought in contact with the 

 inventions and contrivances of man, it not unfrequently 

 breaks down. The lighthouses along our coasts are period- 

 ically besieged by birds at night, many of them being killed 

 in striking the lamps during the spring and autumn migra- 

 tion. Innumerable instances might be forthcoming to prove 

 the disturbing influence of man upon instinct. My special 

 object this evening in bringing this subject before the Society 



