Meteorological Ohservatmis. 159 



four revolving mirrors, each performing 1000 rotations in a second. 

 By emploj'ing a medium of greater refractive power than water, as 

 the essential oils or sulphuret of carbon, a still greater alteration in 

 the velocity of the transmitted ray will be observed, being accele- 

 rated on the corpuscular, and retarded on the undulatory hypothesis. 



Another mode of testing the truth of the two theories, pro- 

 posed by M. Arago, is founded upon the different velocities of the 

 coloured rays of the spectrum, whilst traversing refracting media. 

 If, therefore, a beam of white light be made to traverse a long tube 

 filled with a highly dispersive fluid, as sulphuret of carbon, the dif- 

 ferent coloured rays will not reach the revolving mirror simultaneously, 

 and a spectrum will be produced. So far, the same result occurs on 

 both theories ; but on watching the reflected images, a diflferent ar- 

 rangement of the colours will be observed, and the violet or red 

 band will be observed, in the reflected image, to be situated to the 

 right or to the left, according to the direction of the rotation of the 

 mirror. The order in which the colours appear, the direction of the 

 rotation remaining the same, will be precisely the reverse on the 

 undulatory, to that on the corpuscular theory. 



It is of course obvious that great practical difliculties lie in the 

 way of submitting M. Arago's ingenious views to the test of experi- 

 ment, and hitherto no attempt appears to have been made to over- 

 come the difficulties connected with the construction of the apparatus 

 required for these interesting experiments. 



METEOROLOGICAL OBSERVATIONS FOR DEC.^ 18.39. 



Cliiswick. — Dec. 1 — S. Dense fog. 4. Frosty : fine. 5. Slight haze : fine. 

 6. Foggy. 7. Dense fog: fine: frosty at night. 8 — 10. Hazy. 11. Fine: hazy: 

 rain. 12. Cloudy and windy. 13. Overcast : heavy rain at night. 14. Fine. 

 15. Frosty : hazy : rain. 16. Hazy: fine. 17. Fine. 18. Hazy. 19. Cloudy, 

 rain. 20, Rain. 21. Cloudy: rain. 22, Rain: fine. 23. Fine: very mild for 

 the period of the season : rain at night. 24. Boisterous with rain. 25. Very fine. 

 26. Heavy rain. 27. Rain : hazy. 28. Frosty : line. 29. Clear and frosty. 

 SO. Frosty and foggy. 31. Overcast: fine. 



Boston. — Dec. 1. Fine. 2. Foggy: rain p.m. 3. Cloudy: rain a.m. 4. 

 Foggy. 5. Cloudy: rain P.M. 6,7. Foggy. 8,9, 10. Cloudy. 11. Cloudy: 

 rain early A.M.: rain p.m. 12. Fine: rain p.m. 13. Fine. 14. Cloudy. 15. 

 Fine. 16. Foggy; 17. Fine. 18. Stormy: rain p.m. 19,20. Cloudy: rain 

 early A.M. : rain p.m. 21. Fine: rain p.m. 22. Cloudy: rain p.m. 23. Fine: 

 rain P.M. 24. Cloudy. 25. Fine. 26. Fine: rain p.m. 27. Foggy. 28,29. 

 Fine. SO. Fine: hail and rain p.m. 31. Cloudy. 



Applegarfh Manse, Dumfries-shire. — Dec. 1. Clear and sunny. 2. Calm and 

 clear: hard frost. 3. Dull: raw day. 4. Dull, but dry. 5. Frost a.m.: thaw 

 p.m. 6. Dull moist day : hoar frost early a.m. 7. Dull and cloudy, but dry : 

 hoar frost A.M. 8. Fine day : slight hoarfrost. 9. Quiet and cloudy. 10. 

 Quiet and cloudy : freezing p.m. 11. Fine day : wind rose p.m. 12. Heavy 

 rain in the afternoon. 13. Fine morning : rain afternoon. 14. Moderate day : 

 slight frost preceding night. 15. Foggy: slight frost preceding night. 16. 

 Fine : slight frost early a.m. 17. Raw and cold. 25. Stormy day of wind and 

 rain. 26. Clear day : frosty morning. 27. Snow in the evening, and frost all 

 day. 28. A little more snow: hard frost p.m. 29. Clear and calm and frosty. 

 SO. Looking dull a.m. : sleet and rain p.m. 31. Heavy rain all morning : cleared 

 up P.M. 



Sun 20 days. Rain 9 days. Snow 3 days. Frost and hoar frost 1 3 days. 



Wind easterly 13 days. North-east 4 days. Southerly 4 days. Westerly 2 

 days. 



