*

ASSISTED BY DR. BLACK.

141

"If this reciprocating engine should not [answer,] it must be [from] some mechanical difficulty, which, I think, we may certainly get the better of. If Dr. Small should choose to be concerned with you in this, I have reason to think it would be agreeable to Dr. Roebuck, and would be highly so to me. If you should not choose to engage with this affair in its present state, or at any rate, you will let this letter remain a secret except to Dr. Small.”

It was in the meantime determined, while awaiting Mr. Boulton's reply, that the patent should be taken out, so as at all events to secure the property in the new engine to its inventor, and those who might be associated with him in its manufacture. On the 5th of January, 1769, accordingly, the memorable patent for ""

A NEW METHOD OF LESSENING THE CONSUMPTION OF STEAM

AND FUEL IN FIRE-ENGINES," was obtained; and the relative specification in due course, that is, within four months afterwards, enrolled. Dr. Roebuck had agreed, in consideration of receiving an assignation of two-thirds of the property of the invention, to defray the debt (of nearly 10002.) incurred by Mr. Watt in making the previous experiments, and also the expense of the patent, and of any further experiments; while Mr. Watt was "to attend and conduct the experiments." In reality it turned out that Mr. Watt had to meet all the expenses with the exception of the debt of 1000l., which Roebuck took, as agreed, upon himself; and although the funds thus required were not of any very large amount, they still were such as Mr. Watt might have had extreme difficulty in providing out of his small profits in the regular way of his business. We have ascertained that, at least to nearly the whole extent required for obtaining the patent, they were advanced by Dr. Black; who in this, as well as in many other ways, had both the ability and the inclination to promote the success of the labours of his young friend.

We nced scarcely add that the sum thus provided was gratefully repaid, with interest, by Mr. Watt, when days of greater affluence had dawned upon him. But we feel pleasure in making

known this instance, which we believe is not a solitary one, in which Dr. Black showed himself ready to aid a deserving neighbour less opulent than himself; as it has been alleged,—probably not altogether without reason,—that the learned Doctor was somewhat penuriously attached to the saving of money. The considerable fortune which he bequeathed to his relations, (upwards of 20,000l.,) certainly bore witness to his prudence as a financier no less than to his success as a physician; but on this subject we cannot do better than quote from one of his letters to Mr. Watt, written in the last year of his life,* in which he says, "You should study now to enjoy relaxation from business, and the amusements which are the most suited to your taste; but above all, relaxation and ease, and gentle exercise, and change of air. You need not be anxious now about your fortune. It is already abundant, and it will increase constantly, even while you are sleeping. It is, however, one of the follies of old age to be too intent on the accumulation of riches; and I feel in myself a degree of that inclination. Those of us especially who have made a little fortune by our own industry, set a high value on riches on account of the labour which they have cost us; and when time has put an end to other enjoyments, one of our greatest pleasures is to increase the hoard. We do not consider that it is already sufficient for every reasonable purpose. We have acquired a taste and a habit which we indulge. If you can be amused with the works of Horace, you will find in them many pleasant allusions to this folly, and ingenious expositions of the absurdity of it." We can hardly imagine either a more pleasant allusion to the foible in question, or a more sound exposition of the absurdity of it, than those thus delivered by the amiable and philosophic Doctor ; whose discourse sounds partly as a warning against the sin, and partly as a rather complacent confession of its commission.

* Dr. Black to Mr. Watt, Edinburgh, 1 Feb., 1799.

CHAPTER XIV.

SPECIFICATION OF THE PATENT OF 1769-INTERRUPTED NEGOTIATIONS-CONTINUED EXPERIMENTS-EXPANSIVE POWER OF STEAM-SUCCESSFUL TRIAL OF ENGINE AT NEGOTIATIONS WITH SOHO-CONTINGENT

KINNEIL-PIPE-CONDENSER-FURTHER

AGREEMENT WITH DR. ROEBUCK-POSITION AND CIRCUMSTANCES OF MR. WATT.

WATT, while continuing his experiments at Glasgow, and his preparations for further trials of the engine "in the glen behind Kinneil," where "the burn afforded plenty of cold water" for condensation, and there was greater "freedom from speculation than about Bo'ness," now busied himself in making a draft of the Specification, which had to be given in and enrolled within four calendar months of the date of the Letters Patent. In the preparation of this document, which afterwards became one of great interest in the history of the steam-engine, not only from the nature of its contents, but also from the long and fiercely-contested litigation of which it was the turning point, he received the benefit of the advice of his friends Dr. Small and Mr. Boulton; and the event showed that their enlarged views of the principles on which it ought to be framed, were sound and judicious.

"Mr. Boulton and I," writes Dr. Small to Mr. Watt,* "have considered your paper, and think you should neither give drawings nor descriptions of any particular machinery, (if such omissions would be allowed at the office,) but specify in the clearest manner you can that you have discovered some principles, and thought of new applications of others, by means of both which,

* 5 Feb. 1769.

joined together, you intend to construct steam-engines of much greater powers, and applicable to a much greater number of useful purposes, than any which hitherto have been constructed; that to effect each particular purpose, you design to employ particular machinery, every species of which may be ranged in [one of] two classes: one class for producing reciprocal motions, and another for producing motions round axes.

"As to your principles, we think they should be enunciated (to use a hard word) as generally as possible, to secure you as effectually against piracy as the nature of your invention will allow. You might declare in some such manner as the following:

First, you intend that the vessels in which powers of steam will be employed to work such engines as you may construct, shall be heated, before the working of the engines shall begin, at least as hot as the steam to be conveyed into the vessels, and that this heat of the vessels shall be rendered equable, whilst the engines work, by suffering them to be entered or touched in that time by no substance colder than the steam they are designed to receive, by covering them with materials which allow bodies so covered to cool very slowly, and by proper applications of heated bodies when they may be wanted. The vessels mentioned in this

paragraph you call steam-vessels.

"Secondly, in the engines which you may erect to be worked, either wholly or partially, by condensation of steam, you intend that the steam shall be condensed in vessels distinct from the steam-vessels, though occasionally communicating with them. These vessels you call condensers; and, whilst the engine may be working, you intend to keep the condensers constantly at least as cold as the air then in the neighbourhood of the engines, by applications of water, and other means of cooling heated bodies.

Thirdly, whatever air or other uncondensible elastic vapour may impede the operations of the engines, you intend shall be drawn out by machines in the manner of pumps, to be worked by the engines themselves.

"Fourthly, you intend that on different occasions the necessary steam shall be produced from different substances, solid or

SPECIFICATION OF PATENT OF 1769.

145

fluid, or partly solid and partly fluid, as may be most convenient; and also that the vessels in which the steam shall be produced, (which you call boilers,) shall be of different forms on these differ

ent occasions.

"Fifthly, in many cases you design to employ steam in producing reciprocal motions in a manner like to that in which portions of the atmosphere are now employed in ordinary reciprocating engines, to wit, by pressing at proper times upon pistons of proper structures.

Sixthly, to produce, by means of steam motions round axes, you intend sometimes to employ reciprocatory joined to other machines, but more frequently steam-vessels of forms fitted to different purposes. These steam-vessels will be mounted on axes, and will contain weights, either solid or fluid, or partly solid and partly fluid; which weights, or the centres of their gravity, being constantly, whilst the engines work, pressed by steam beyond planes perpendicular to the horizon, and in which planes the axes will lie, will cause motions of the steam-vessels.

"Seventhly, in these last-mentioned engines, in which steamvessels must move round axes, on some occasions you intend to use the condensers described above; but on others, to discharge the steam from the steam-vessels, through proper outlets, into the atmosphere.

"Lastly, to render pistons and other parts of the machinery air and steam-tight, instead of water you design to employ paper and pasteboard prepared with oils, oils themselves, or fat of animals, quicksilver, or melted metals."

Dr. Small adds, in a part of his letter written two days later, "I am certain that, from such a specification as I have written, any skilful mechanic may make your engines, although it wants correction; and you are certainly not obliged to teach every blockhead in the nation to construct masterly engines." The form of specification thus prudently recommended, differed but slightly from that ultimately adopted, which was signed and sealed on the 25th of April, and enrolled on the 29th of that month.