I have purposely delayed writing until I could communicate to you some intelligence of importance concerning the new Pneumatic Institution. The speedy execution of the plan will, I think, interest you both as a subscriber and a friend to science and mankind. The present subscription is, we suppose, nearly adequate to the purpose of investigating the medicinal powers of factitious airs. It still continues to increase, and we may hope for the ability of pursuing the investigation to its full extent. We are negotiating for a house in Downe Square, the proximity of which to Bristol and its general situation and advantages render it very suitable for the purpose. The funds will, I suppose, enable us to provide for eight or ten patients in the Hospital, and for as many out of it as we can procure. We shall try the gases in every possible way. * * * * * We are printing in Bristol the first volume of the ‘West Country Collection,’ which will, I suppose, be out the beginning of January. * * * * * Believe me, dear Sir, with affection and respect, truly yours, HUMPHRY DAVY. The first two hundred pages of this collection, constituting very nearly half the volume, consist of essays of Davy on ‘Heat, Light, and the Combinations of Light,’ on ‘Phos-Oxygen or Oxygen and its Combinations,’ and on the ‘Theory of Respiration.’ He wrote on February 22, 1799, to Davies Gilbert: DEAR FRIEND,--(For I love you too well to call you by a more ceremonious name), I have delayed writing to you, expecting that some of our experiments would produce results worthy of communication. I am now as much convinced of the non-existence of caloric as I am of the existence of light. Our laboratory in the Pneumatic Institution is nearly finished. I hope the gaseous oxide of azote will prove to be a specific stimulus for the absorbents. * * * * * I know of little general scientific news. Berthollet makes sulphuretted hydrogen out to be an acid. * * * * * I remain, with affection and respect, yours, HUMPHRY DAVY. Again on April 10, 1799, to Mr. Gilbert, writing of light and heat, he said: The supposition of active powers common to all matter from the different modifications of which all the phenomena of its changes result, appears to me more reasonable than the assumption of certain imaginary fluids, alone endowed with active powers, and bearing the same relation to common matter as the vulgar philosophy supposes spirit to bear to matter. It is only by forming theories, and then comparing them with facts, that we can hope to discover the true system of nature.