XIV.]

WATT DECLINES TO JOIN MILLER.

175

experiments, immediately after such a promising beginning, has frequently been regarded as unaccountable. The explanation of the matter is very probably to be found in the attitude assumed by Boulton and Watt. Mr. Cullen of Edinburgh (afterwards Lord Cullen) seems to have taken a lively interest in Miller's experiHe wrote an account of them in the Edinburgh newspapers of the day, and appears to have addressed an application, on the part of Miller, to Boulton and Watt, with a view to engaging them to connect themselves with Miller's undertaking.

ments.

The following reply from Watt to Mr. Cullen, dated April 24th, 1790, throws some interesting light upon the subject:

"DEAR SIR, We have heard of Mr. Miller's ingenious experiments on double ships from Sir John Dalrymple, and also some vague accounts of the experiments with the steam engine, from which we could gather nothing conclusive, except that the vessel did move with a considerable velocity.

"From what we heard of Mr. Symington's engines, we are disposed to consider them as attempts to evade our exclusive privilege; but as we thought them so defective in mechanical contrivance as not to be likely to do us immediate injury, we thought it best to leave them to be judged by Dame Nature first, before we brought them into an earthly court.

"We are much obliged to Mr. Miller for his favourable opinion of us and of our engines, which we hope experience will more and more justify. We are also fully sensible of his kind attentions in offering to associate us in his scheme; but the time of life we have both arrived at, and the multiplicity of business we are already engaged in, must plead our excuse from entering

into any new concern whatsoever as partners,-but as engineers and engine-makers, we are ready to serve him to the best of our abilities, at our customary prices of rotative engines, and to assist in anything we can to bring the scheme to perfection.

"We conceive there may be considerable difficulty in making a steam engine to work regularly in the open sea, on account of the undulatory motion of the vessel affecting the engine by the vis inertia of the matter; however, this we should endeavour to obviate as far as we can.

"It may not be improper to mention that Earl Stanhope has lately taken a patent for moving vessels by steam, but we believe not by wheels. His lordship has also applied to us for engines, but we believe we are not likely to agree with him, as he lays too much stress upon his own ingenuity.

"We cannot conclude without observing that, were we disposed to enter into any new concern, there is no person we should prefer to Mr. Miller as an associate, being fully apprised of his worth and honour, and admirers of the ingenuity and industry with which he has pursued this scheme.

"Permit me now, sir, to return you my thanks for your obliging attention to me, and the trouble you have taken in this affair, and to ask the favour of you to present Boulton and Watt's respectful compliments to Mr. Miller.-Dear Sir, your obliged humble servant, JAMES WATT.

Robert Cullen, Esq., Edinburgh." 1

The manufacture of stationary condensing engines afforded an ample field for all the energies of Boulton and Watt, without the necessity for their entering upon any new and untried courses. Their patent privileges, so long as they remained in force, stood in the way of others disposed to do so.

1 Memorials of James Watt, by George Williamson, Esq., Printed for the Watt Club, 1856, pp. 219, 220.

CHAPTER XV.

CONCLUDING REMARKS REGARDING WATT'S ENGINE.

RIVAL ENGINES.

To the last Watt continued to employ steam of a pressure similar to that which had been used in Newcomen's engines, that is, not more than one or two pounds above the pressure of the atmosphere. Thus the steam engine in the hands of Watt was the perfection of the vacuum engine, which, as we have seen, a long line of inventors had been striving to produce. The steam was now used with the greatest economy compatible with the employment of low-pressure steam; the vacuum was produced under the most favourable conditions. But in bringing the engine into the form which it had now arrived at, Watt had at the same time mastered the difficulties in the way of employing steam of a higher pressure. Nothing now prevented its use above, as well as below, the piston; a stronger boiler only was necessary.

N

That Watt did not employ steam of a higher pressure was not the result of ignorance, as has sometimes been supposed. His objection to it appears to have been founded chiefly on the danger which he feared would attend its use. Yet he took the precaution to include the non-condensing form of engine in his patent of 1769. 'In cases where cold water cannot be had in plenty," he says, "the engines may be wrought by the force of steam only, by discharging the steam into the open air after it has done its office."

A little later we find Boulton urging Watt to employ steam of a higher pressure, on account of its superior economy. In a letter to Watt, dated July 25th, 1776, he writes as follows:

"I did not sleep last night, my mind being absorbed in STEAM; and thus I reasoned in my waking dreams :—

Hence the price of the power of one atmosphere is reduced from 1,012 pence, or shillings, to 272 pence, or shillings, which is almost four times better. Then as to boilers and steam-pipes, let them be as strong as cannon; but as the fire will not be applied so advantageously through thick metal, let it be applied in copper spheres within the water, and then four or five atmospheres will not compress such forms. The great boiler may be framed with scantlings of cast-iron, well screwed together with wrought-iron plates

xv.]

EXPANSIVE WORKING.

179

half-inch thick, well-fitted and screwed within; and then, the greater the elastic force of the steam, the closer they will be pressed, as the lid of a digester is. As to the piston, it may be laid with asbestos cloth, if oakum will not stand the heat, and by this means the present construction of the engine will do. But certainly it's a desirable thing to invent an engine to work with the expansive and contractive power of steam, as I am clear the principle is sound.” 1

Watt appears to have been unmoved by the appeals of his partner to use strong steam, preferring security from accident to increased profits, but the value of working expansively had been well known to him as early as 1769, as appears from one of his letters to Dr. Small.2 About 1776 the engine at Soho was adapted to work expansively, and an attempt was made by Boulton and Watt to apply the principle generally, but they found it necessary to desist, owing to insufficient skill on the part of the enginemen. The expansive principle, however, was included in Watt's patent of 1782 (Fig. 36).

Among the many improvements effected by Watt, with a view to promote economy of steam and fuel in his engines, was the introduction of new forms of valves and boilers.

The valves consisted of circular brass plates made conical at their edges, and ground to their seats with 1 Mechanical Inventions of James Watt, Vol. II., pp. 101-2. 2 Farey on the Steam Engine, p. 339.

3 Smiles's Lives of the Engineers-" Boulton and Watt," ed. 1874, p. 172.