252 Mr Laidlaw's account of the Aurora Borealis 



pecially if in this department he unite, like Tulley, the zeal 

 of the amateur with the skill of the superior artist. 



I intend soon to put to the test of experiment, whether or 

 not the principle of the two aplanatic pencils may be applied 

 to telescopes, in cases in which it is requisite to restrict their 

 length, so as to enlarge their aperture with a corresponding 

 increase of light and distinctness. In the meantime, it would 

 give me pleasure to see that principle demonstrated, if it de- 

 serve it, by some abler hand than mine, and treated in a more 

 rigorous manner than my own limited acquaintance with ma- 

 thematical science qualifies me to undertake. 



(Note A.) The blue down of the Menelaus and the white 

 of the Cabbage Butterfly (Morpho Menelaus and Pieris Bras- 

 sicse) well deserve the place they have acquired as standard 

 tests, especially on account of the respective characters of their 

 transverse tracings. Some of the small oval scales from the 

 body of the Twenty.pl umed Moth (Alucita hexadactyla) are 

 amono- the closest and most elegant in their lines that I have 

 seen ; others are very easily resolvable, and the down has such 

 diversity of form as often to afford within a short space a ready 

 variety of excellent tests. The same is to be said of the scales 

 of Podura plumbea, of which all are difficult, and some seem 

 to defy all powers of definition. 



It may be observed, that with most objects there is such 

 difference between individual specimens of the same kind, that 

 in general the only safe way to determine between two good 

 microscopes, is to apply the same specimen to both, under the 

 same circumstances of power and light. — Phil. Trans. 1830. 



Art. XI. — Account of the Aurora Borealis seen in Roxburgh- 

 shire on the 5th of October 1830. By Mr W. Laidlaw, 

 Kaeside. 



On Friday evening, the 17th September, an uncommon form 

 of the aurora borealis was observed all over the country. It 

 was in the shape of a luminous white arch, and stretched from 

 W. bv S., to E. by N. nearly, ending on the E. in a pencil- 

 formed point, and was accompanied by pale streamers in the 



