Portraits in Daguerreotype : — Meteorological Observations. 535 
That chromate of lead is very easily converted by means of carbon 
and hydrogen into a mixture of oxide of chrome and metallic lead. 
This mixture by heating is in a state to combine with oxygen ; 
and this combination takes place not only with the metallic lead, 
but also with the oxide of chrome. 
By heat alone it is very difficult to deprive chromate of lead of 
oxygen. It is at first converted into a mixture of basic chromate 
of lead and oxide of chrome : in order to reduce all the chromic 
acid into oxide of chrome, an uncommonly highly temperature is re- 
quired. 
When a mixture of oxide of chrome and oxide of lead is heated, 
it is also converted into basic chromate of lead and oxide of lead. 
It is therefore chromate of lead, which is often employed in or- 
ganic analysis, from which this latter mixture is derived . — Journal 
fiir PraktiscTie Chemie, No. 2. 1840. 
PORTRAITS IN DAGOERREOTYPE. 
Professor Draper, of the University of New York, informs us in 
a note dated March 31st, that he has succeeded during the winter 
in procuring portraits by the Daguerreotype, and that they have all 
the beauty and softness of the most finished mezzotint engraving, and 
only require from 20 to 45 seconds for execution. 
METEOROLOGICAL OBSERVATIONS FOR APRILj 1840. 
Chiswick. — April 1. Slight rain ; cloudy. 2. Hazy : very fine. 3. Cold dry 
haze : frosty at night. 4 — 6. Very fine. 7. Fine : stormy showers at night. 
8. Slight showers. 9. Cloudy and cold. 10 — 12. Very fine. 13 — 17. Fine but 
very dry. 18. Clear, hot and dry. 19. Hazy : very fine. 20. Very fine. 21 — 
23. Cloudy and fine. 24. Very fine. 25. Very hot, nearly cloudless, and ex- 
cessively dry. 26, 27. Hot and dry. 28. Excessively hot for the period of the 
season, thermometer 81° in the shade. 29,30. Very fine: hot and dry. This 
month is remarkable for the limited quantity of rain and for a high temperature ; 
the latter being the consequence chiefly of a powerful direct solar heat, which 
overcame likewise the counteracting effects of north and north-east winds, for 
they were in fact more prevalent than those from the opposite direction. 
Boston. — April 1. Cloudy; rain p.m. 2. Rain. 3 — 5. Fine. 6. Cloudy. 
7. Cloudy : stormy with rain p.m. 8. Cloudy: hail and rain p.m. 9 — 11. Fine. 
12. Rain: rain early a.m. 13 — 19. Fine. 20 — 24. Cloudy- 25 — 29. Fine. 
30. Cloudy. 
Applegarth Manse^ Durrjries-shire. — April 1. Mild day with a shower. 2. Keen 
and cold but dry. 3, 4. Dry and more temperate. 5. Fine day after a very 
slight shower. 6. Stormy day with showers, though slight. 7. Keen cold day. 
8. More moderate. 9. Fine mild day. 10. The same: slightly moist and 
cloudy. 1 1. Drizzling all day, but very lightly. 12. Fine though cold : slight 
rain P.M. 13. Fine soft slight rain. 14. Charming spring day. 15. The same: 
with frost rime A.M. 16,17. Fine but coldish : frost rime again. 18. Very fine 
warm day. 19. The same : white rime a.m. 20. The same : slight showers 
P.M. 21. The same: gentle shower. 22. The same : moisture. 23. Dry but 
threatening. 24. The same : cleared up. 25 — 28. Beautiful day. 29. The 
same, but cloudy. SO. The same : very warm. 
Sun shone out 29 days. Rain, very slight, fell 6 days. Frost, rime 4 days. 
Wind north 1 day. North-east ^ day. East-north-east 2 days. East 3 days. 
East-south-east 1 day. South-east ^ day. South-south- east 2 days. South 7 
days. South-south-west 1 day. South-west 7§ days. West-south- west 1 day. 
West 2§ days. North-west 1 day. 
Calm 15 days. Moderate 8 days. Brisk 3 days. Strong breeze .3 days. 
Boisterous I day. 
