584 
WATT. 
order of ensatae, irides (Juss.J —Generic Character. Calyx: 
spathes pressed close, mortified at top, for tlie most part 
coloured. Corolla curved back; tube slender; throat cup- 
cylindric; border six-parted, the parts spreading-regular or 
subbilabiate, equal or nearly so in breadth, quite equal in 
length. Stamina: filaments three, growing to the tube, but 
distinct from the throat. Pistil: germ inferior, triangular- 
cylindric. Style simple, filiform, erect. Stigmas three, 
slender, bifid. Pericarp: capsule stiff-leathery, triangular- 
cylindric, drawn to a point at each end. Seeds numerous, 
somewhat oblong.— Essential Character. Corolla six- 
parted, spreading or subbilabiate, equal. Stigmas three- 
bifid. Capsule triangular-cylindric, attenuated at each 
end. ’ , 
1. Watsonia aletroides, or aletris-like Watsonia.—Corollas 
somewhat drooping; tube nearly equal to the spathe; throat 
almost four times as long as the short ovate equal segments 
of the border. 
2. Watsonia roseo-alba, or long tube Watsonia.—Corolla 
regular; tube twice as long as the spathe throat or border; 
segments equal, spread out, flat acuminate; stamens equal to 
the throat. 
3. Watsonia iridifolia, or flag-leaved Watsonia.—Corolla 
refracted; tube erect, longer than the spathe, equal to the 
segments, which spread out very wide obliquely, indistinctly 
two-lipped, oval-oblong somewhat sharp equal to the throat. 
There are two varieties. 
4. Watsonia brevifolia,or short-leaved Watsonia.—Leaves 
very low somewhat oblong shining; tube throat and border 
equal in length ; segments regular-spreading, the inner ones 
wider; stamens resupine declined. 
5. Watsonia marginata, or long-spiked Watsonia.—Leaves 
thick at the edge; spike elongated composed of close-pressed 
spikelets confluently continuous; border regular; throat 
short, six-toothed within; stamens erect, looking three ways. 
6. Watsonia laccata, or lake-coloured Watsonia.—Leaves 
narrower, vertically, ensiform, strict, twisted a little; spathe 
tube throat and border equal; pistil nearly equal to the 
segments which are acute alike and regularly spreading. 
The root in this elegant genus is tuberous-tunicated, 
hemispherical, toothed at the edge. Scape very stiff, fre¬ 
quently inclined to woody, simple, or little branched. 
Leaves ensiform, attenuated at each end, often shining. 
Flowers in loose terminating spikes.—All the species are 
natives of the Cape of Good Hope. 
Propagation and Culture. —See Antholyza. 
WATT (James), was born at Greenock, the 19th January, 
1736. He received the rudiments of his education in the 
public schools of his native town; but, from the extreme de¬ 
licacy of his constitution, was with difficulty enabled to 
attend the classes, and owed much of his acquirements to his 
studious habits at home. Little more is known of his early 
years, than that, from the first, he manifested a partiality for 
mechanical contrivances and operations, and frequently em¬ 
ployed himself in that way. The desire of improvement in 
an art then little practised in Scotland, induced him to go to 
London in his eighteenth year, and there to place himself 
under the tuition of a mathematical instrument-maker; but 
he remained little more than a twelvemonth, the infirm state 
of his health compelling his return to the paternal roof. 
In that short period, he appears to have made great profi¬ 
ciency, and continued, after his return to Scotland, to perfect 
himself in this art, both at home and on his visits to his mo¬ 
ther’s relations at Glasgow, where it was his wish to establish 
himself. But some opposition being made by the corpo¬ 
rations, who considered him as an intruder upon their pri¬ 
vileges, the Professors of the College took him under their 
protection, and accommodated him with an apartment and 
premises for carrying on his business within their precincts, 
with the title and office of Mathematical Instrument-maker to 
the University. This took place in 1757. Mr. Watt now 
applied sedulously to business, and in the few intervals which 
its concerns, and ill health allowed, cultivated those various 
talents which distinguished him in after-life. 
He remained in the college until some time in the year 
1763, when he removed into the town previous to his mar¬ 
riage with his cousin, Miss Miller, which took place in the 
summer of the following year. 
The Steam-Engine had been a frequent subject of conver¬ 
sation between Mr. Robinson and himself, and the former 
had suggested the possibility of its application to the moving 
of wheel-carriages. About the year 1761 or 1762, Mr. Watt 
had tried some experiments on the force of steam in a Papin’s 
digester, and had constructed and worked with strong steam 
a small model, consisting of an inverted syringe; the bottom 
of the rod of which was loaded with a weight, alternately 
admitting the steam below the piston, and letting it off to the 
atmosphere. Observing the imperfections of this construc¬ 
tion, he soon abandoned it; but the attention necessary to 
be bestowed upon his business prevented his reconsidering it, 
until the winter of 1763-4, when he was employed by the 
Professor of Natural Philosophy to put in order a working 
model of a steam-engine upon Newcomen’s construction. 
When he had repaired it and set it to work, he found that 
the boiler, though large in proportion to the cylinder, was 
barely able to supply it with steam for a few strokes per 
minute, and that a great quantity of injection water was re¬ 
quired, though it was but lightly loaded by the pump attach¬ 
ed to it. It soon occurred, that the cause lay in the little 
cylinder (two inches diameter, six inches stroke), exposing 
a greater surface to condense the steam than the cylinders of 
larger engines did, in proportion to their respective contents. 
By shortening the column of water in the pump, less steam 
and less injection water were required, and the model worked 
at a proper speed. Thus the purpose for which it was put 
into his hands was accomplished; and with this mode of 
accounting for the defect and this result, most artists would 
have been satisfied. Not so Mr. Watt. He had now be¬ 
come aware of a great consumption of steam, and his curi¬ 
osity was excited to a more accurate investigation of the 
causes, in which he proceeded in a truly philosophical man¬ 
ner. The cylinder of his small model being of brass, he 
conceived that less steam would be condensed by substituting 
cylinders of some material which would transmit heat more 
slowly. He made a larger model with a cylinder (six 
inches diameter, and one foot stroke) of wood, soaked in oil, 
and baked to dryness. He ascertained, from experiments 
made with boilers of various constructions, that the evapo¬ 
ration of boiling water is neither in proportion to the evapo¬ 
rating surface, nor to the quantity of water, as had been 
supposed, but to the heat that enters it; and that the latter 
depended chiefly on the quantity of surface exposed to the 
action of the fire. He likewise determined the weight of 
coal required for the evaporation of any given quantity of 
water. Being convinced that there existed a great error in 
the statement which had been previously given of the bulk 
of water when converted into steam, he proceeded to ex¬ 
amine that point by experiment; and discovered, that water, 
converted into steam of the heat of boiling water, was ex¬ 
panded to 1800 times its bulk : or, as a rule for ready calcu¬ 
lation, that a cubic inch of water produced a cubic foot of 
steam. He constructed a boiler to be applied to his model, 
which should show, by inspection, the quantity of water 
evaporated, and, consequently, would enable him to calcu¬ 
late the quantity of steam used in every stroke of the engine. 
This he now proved to be several times the full of the cylin¬ 
der. He also observed, that all attempts to improve the 
vacuum, by throwing in more injection water, caused a 
disproportionate waste of steam: and it occurred to him, that 
the cause of this was the boiling of water in vacuo at very 
low heats (recently determined, by Dr. Cullen, to be under 
100 °); consequently, at greater heats, the injection water 
was converted into steam in the cylinder, and resisted the 
descent of the piston. He now perceived clearly, that the 
great waste of steam proceeded from its being chilled, and 
condensed by the coldness of the cylinder before it was 
sufficiently heated to retain it in an elastic state; and that, to 
derive the greatest advantage, the cylinder should always be 
kept as hot as the steam that entered it, and that, when the 
steam was condensed, it should be cooled down to 100 °, or 
lower 
