TYNDALL. — OBSERVATIONS IN ARCTIC REGIONS. 35 



9. The condition of the rocks and hills adjacent to existing 

 glaciers ought to be examined, with a view to decide whether the 

 glaciers, in former times, extended beyond their present limits. 



10. The veining of the ice, at the ends of the glaciers, ought to 

 be sketched and described. 



11. Observations might be made on the colour of the ice. It 

 would also be interesting to determine the colour of the sky on 

 different days by a cyanometer ; and how the colour varies with 

 the zenith distance. Various cyanometers are described by 

 Dr. Hermann Schlagintweit in the Philosophical Magazine for 

 1852, vol. iii. p. 92. 



12. The polarization of the sky, and the determination of the 

 neutral points in the Arctic firmament, might also be made an 

 interesting subject cf observation. 



13. The presence or absence of germs in the Arctic air might 

 be ascertained by experiments similar to those of Pasteur upon 

 the Mer de glace. 



14. The range of a sound of a definite character on different 

 days, and at different hours of the same day, ought to be deter- 

 mined. I have myself derived much instruction from experiments 

 made — 



1. With a dog-whistle. 



2. With an open organ-pipe producing from 300 to 400 

 waves a second ; a pistol fired with a definite charge would 

 also be useful. It would also be easy to fit up a bell with 

 a hammer to deliver upon it a stroke of constant strength. 

 Mr. Tisley would prepare such a bell immediately. In 

 all cases the state of the weather, when experiments on 

 sound are made, ought to be noted. 



15. The aerial echoes ought to be observed; here the sound 

 of a cannon will be necessary. The echoes of a cannon, fired to 

 windward, ought to be compared with those of the same, or of a 

 similar cannon, fired to leeward. 



16. The range of two sounds differing in pitch, ^ay an octave 

 apart, ought to be determined; the experiments ought to be 

 repeated on different days, with the view of determining whether 

 the same sound has, at all times, the greatest range. 



I beg to enclose with these suggestions : — 



1. A copy of a paper on the Physical Properties of Ice ;* 



2. A copy of a paper on the Atmosphere as a Vehicle of 

 Sound ; 



3. A copy of a book entitled " Forms of Water ; " 

 from which various hintg and suggestions may be derived. 



* The internal structure of the Arctic ice ought to be explored by con- 

 centrated sunbeams, in the manner indicated in this paper. 



