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modifications, — the vibratory or permanent, and the undulatory or transient state; and that the forces which produce these several effects differ from each other only in the frequency of their undulations or vibrations.

Such are the conclusions at which the all-inquiring Dr. Young arrived in 1801, on a subject which in 1850 is proposed for our investigation. Well may Admiral Smyth say, “How strange it is that we are still but half-acquainted with the results of his powerful mind I”

Of course I shall not quarrel with you if you do not accept his conclusions, totidem verbis; because, as I am aware, you see reasons for believing that light, or that agent which affects the organs of sight, is broadly distinguished from those rays which bring heat from its solar source, and both of these classes form those which produce, in the constitution of bodies, those singular changes which are more particularly the objects of your study. But Sir John Herschel has shown that, by certain artifices, even the extreme rays may be rendered visible; and Dr. Young, by an experiment most ingenious, and to his own mind, at least, most conclusive, has demonstrated the analogy of the invisible with the visible rays. I feel sure, therefore, that while adducing and discussing the proofs of your own theory, you will be glad to take the opportunity afforded by your second edition of placing Dr. Young's name in the niche which Fame has left empty.

Believe me to be, my dear Sir,

Very truly yours,
To Robert Hunt, Esq.

J. B. Reade.

No. III. (Referred to from Preface and page 225.) ON THE USE OF BLUE GLASS IN ACCELERATING GERMINATION.

Edinburgh, 1. George the Fourth's Bridge,

September 8. 1853. MY DEAR SIR, – I am favoured with yours of the 5th, relative to my practical experience in the effect of the chemical agency of coloured media on the germination of seeds and the growth of plants.

I must first explain that it is our practice to test the germinating powers of all seeds which come into our warehouses before we send them out for sale; and, of course, it is an object to discover, with as little delay as possible, the extent that the vital principle is active, as the value comes to be depreciated in the ratio it is found to be dormant. For instance, if we sow 100 seeds of any sort, and the whole germinate, the seed will be the highest current value; but if only 90 germinate, its value is 10 per cent. less ; if 80, then its value falls 20 per cent.

I merely give this detail to show the practical value of this test, and the influence it exerts on the fluctuation of prices.

Our usual plan formerly was to sow the seeds to be tested in a hotbed or frame, and then watch the progress, and note the results. It was

usually from eight to fourteen days before we were in a condition to decide on the commercial value of the seed under trial.

My attention was, however, directed to your excellent work, “ On the Physical Phenomena of Nature," about five years ago, and I resolved to pat your theory to a practical test. I accordingly had a case made, the sides of which were formed of glass coloured blue or indigo, which case I attached to a small gas-stove for engendering heat ; in the case shelves were fised in the inside, on which were placed small pots wherein the seeds to be tested were sown.

The results were all that could be looked for: the seeds freely germinated in from two to five days only, instead of from eight to fourteen days as before.

I have not carried our experiments beyond the germination of seeds, so that I cannot afford practical information as to the effect of other rays on the after culture of plants.

I have, however, made some trials with the yellow ray in preventing the germination of seeds, which have been successful; and I have always found the violet ray prejudicial to the growth of the plant after germination. I remain,

My dear Sir,

Very faithfully yours, To Robert Hunt, Esq., Hull.

CHARLES Lawson,

No. IV.

ON THE GLASS IN THE PALM HOUSE OF THE ROYAL GARDENS

AT KEW.

(Referred to from Preface.)

December 6. 1845. Sir, -I am directed by Lord Lincoln to refer to you the accompanying papers relative to the proposed introduction of coloured glass into our new Palm House at Kew, and I am requested that they may be referred to Mr. Hunt, for the benefit of his well-considered opinion, in the shape of a report.

[Signed] T. S. PHILLIPS. Sir Henry De la Beche.

Royal Gardens, Kew,

Nov. 29. 1845. My Dear Sir, — The more I think and inquire upon the subject of coloured glass for the Palm Stove, the more I am struck with its importance, especially as connected with so vast a concern as we are erecting. White glass does occasionally scorch the foliage of the plants. Stained or coloured glass does act upon vegetation, as has been clearly ascertained by Mr. Hunt, in his ingenious experiments; a gentleman, I under

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stand, in one of the departments of the Woods and Forests — the Economic Museum. May I be pardoned, then, if I return the enclosed unreported upon, and take the liberty of suggesting that Mr. Hunt be consulted on this important question. Dr. Lindley would not give an opinion, and he said that Mr. Hunt was the only person in the Kingdom competent to do so. Mr. Hunt, however, should know that it is not with deeply coloured glass that we have to do, but just so much stained (if staining will have the effect) as will deprive the glass of its scorching character, and not affect the vegetation. The tint most recommended is a faint purple.

[Signed] W.J. Hooker.

Edinburgh, 15th November, 1845. SIR, - I beg leave to take the liberty of just mentioning I arrived here to-day from Haddon House, where I am erecting additional works for the Earl of Aberdeen, who has kindly said he would be happy to recommend me to the English ministers of the Continent of any capital I may wish to visit ; and as I hope (D. V.) to be in London next week, with a view of going to Antwerp, and possibly to Bohemia, in pursuit of a very superior coloured glass, the violet tinge; or azure hue, which I understand will be a wonderful improvement for the Royal Palm House and Inner Circle Winter Garden, and, indeed, all horticultural structures, as it beautifully softens the light, and hinders the rays of bright sunshine destroying as much as it does when transmitted through the clear glass, which is found to scorch and wither the tender foliage, as they first appear, and subsequently the blossoms, except they are most carefully blinded by some artificial means. As I am most solicitously anxious to be the first to introduce this desideratum in conservatories, and more particularly in those two I feel myself so very highly honoured to erect-at Kew and Regent's Park - and being of such immense magnitude, the improvement would be so immense, as well to render them additionally enjoyable to visit and walk in as for the plants, &c., &c.

[Signed] RICHARD TURNER. Alexander Milnes, Esq.

Memorandum respecting the Coloured Glass most favourable for Glazing

a Hot or Greenhouse. The consideration of the question as to the applicability of coloured glass to horticultural purposes resolves itself into two or three particular points to which it is necessary every attention should be given,

In the first place, we have to consider the conditions required for healthful vegetation. In the second, to examine how far these conditions are met by the use of media which will transmit certain classes of the solar rays to the abstraction of others; and if coloured glasses admit the

ABSORPTION of carbonic acid by leaves, 243. | Becquérel discovers dark lines of chemical Absorptive powers of yellow glass, 309.

spectrum, 49. of red glasses, 321.

his researches, 113. of green glasses, 923.

modifies Ponton's process, 185. Acetate of mercury, 288.

on solar phosphori, 271. Actinic influence absorbed, 287.

his experiments, 294. rays accelerate germination, 225.

on the absorption of the most power, variations in, 357, 363.

refrangible rays, 321. Actinism, polarization of, 333.

obtains colour on bis photoits relative quantity in sun

graphic plates, 340. beam, 359.

Beetroot, spectrum on juice of, 205. Actinized silver, &c., 289.

Benzoate of the oxide of silver, 129. Agarics, phosphorescence of, 275.

of hydruret of benzule and niAgaricus muscarius grown in moonlight,

trate of silver, 131. 240.

Berard on chemical action of sun's rays, 20. Air, absorptive power of, 357.

on maximum of heat in the specAlbumen on glass used, 138.

trum, 52. photographic process, 87.

on magnetic power of light, 296. Alchymists observe the blacking of horn

on the double refraction of the silver, 5.

chemical rays, 332. Amaranthus, globe, spectrum formed on the, Bernard on the spectrum, 41. 204.

Berres, Dr., on fixing Daguerréotypes, 109. Ammonia oxide of silver, 73.

Berthollet and Biot report on Berard's Amphitype, the, of Sir J. Herschel, 171. experiments, 20. Analysis of the sunbeam, 36.

Berzelius, on the action of light on the salts Ancient explanation of vision, 3.

of gold, 19. Animal and vegetable kingdoms, 245.

on magnetism by light, 298. Animals, phosphorescent, 274.

Biot, M., on bromide of silver, 119. Aquatic plants, Priestley on, 208.

his polariscope employed in exArago, M., on the chemical rays, 351.

periments on actinism, 335. Report on the Daguerréotype, 366.

on vision, 347, Archimedes knew the laws of refraction, 3. Bitumen of Judea, employed by Niepce, 31. Arsenicalis, liquor, 133.

in heliography, 189. Asphaltum, employed by Niepce, 31.

Blackburn's theory of light, 20. Atmospheric changes, influence of, 365. Bleaching action of iodides, 96. Aurotypes, 148.

power of spectrum, 98. Autumn, sunshine in, 240.

Blue cobalt glass, absorptive power of, 327.

Böckman on the action of spectrum on Baldinus discovered phosphorescent bodies, 5. phosphorus, 15. Barium, chloride of, a colorific agent, 63. Boetius de Boot on gems, 4 sulphuret of, 271.

Bolognian stone, 5. 271. Barley, malted and unmalted, 241.

Boyle on the light of the planets, 7. Bauer and Niepce, correspondence of, 25.

on phosphori, 270, Baumgartner, M., magnetizes steel wire by Brassica napus, growth of, 221. light, 297.

Brayley, Mr., lectures on Mr. Reade's Bayard, M., on pictures produced with process, 85. bromide of silver, 121.

Brewster, Sir D., on the compound nature Beccaria, Father, on phosphori, 271.

of light, 40.

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