GRO 
Grodae, GRODNO, is a town of Poland, in Lithuania, and, 
Groin’. with the exception of Wilna the capital, is the most im- 
portant place in that province. It is now a frontier 
town in the Russian, division of Poland. It is built 
upon an eminence which overlooks the river Niemen, 
which is here a broad, clear, and shallow stream. Grod- 
no is a large and straggling place, and has the appear- 
ance of a town in decay. The few houses that are in 
‘ood repair, form a singular contrast with the wretched 
Fabitations, the falling houses, the ruined palaces, and 
the magnificent gateways, which are every. where to be 
seen. Some remains of the old palace, in which the kings 
formerlyresided during the diets, are still to be seen upon 
a hill of sand, rising abruptly from the river, and form- 
ing part of the bank. The new palace is opposite to 
this hill. It was built, but never inhabited, by Augus- 
tus III, and became the temporary residence of Sta- 
nislaus Augustus after his abdication. It contains the 
apartments for the meeting of the diets. The late 
King of Poland established at Grodno a royal academy 
of physic for Lithuania, in which ten students are in- 
structed in medicine, and twenty in surgery, and are 
lodged, boarded, and taught at the royal expence. 
The physic garden contained 1500 exotic plants, when 
Mr Cox passed through the town in 1778. The prin- 
cipal manufactures here, are cloth and camlets, linens 
and cottons, silk stuffs, embroidery, silk stockings, hats, 
lace, fire arms, needles, cards, bleaching wax, and car- 
riages. They were chiefly established by the king in 
1776, and in 1778 they were carrying on in wooden 
sheds, built by Augustus III. for stables, which were 
eonverted into temporary working looms, and dwelling 
houses for the workmen. The establishment was sub- 
sequently remoyed to Lossona, a village near Grodno, 
where convenient buildings were erected at the pub- 
lic expence, The country furnishes a sufficient supply 
of wool, flax, hemp, beavers’ hair, and wax, for the ma- 
nufactories that require these articles; but the silk, 
cotton, iron, colours, gold, and silver, for the embroi- 
dery, and the fine thread from Brussels, are all articles 
of import, Three thousand persons are employed in 
these manufactories, including those in the neighbour- 
ing villages who spin linen and worsted. Seventy fo- 
reigners direct the different branches, and the rest are 
natives. Grodno contains nine Catholic churches, and 
two Greek churches. The population consists of 3000 
Christians, exclusive of those engaged in manufactures, 
and 1000 Jews, See Cox’s Travels in Poland, Sc. vol. i. 
p- 220, 223, reat ty gil 
GROINS. In our article Carpentry, Book iii. p. 
522, &c. we have already treated the subject of groins 
at some length. We proposed, under the present head, 
to have investigated the subject of Domes, from which 
we have made a reference ; but we have found it ne- 
cessary to include this subject under that of Roors, to 
which the reader is referred. 
In the article Canpenrry, we have mentioned the 
great improvement in the construction of brick groins, 
rising from rectangular piers, as made by Mr loomee 
Tapper. The following account of this improvement 
has been drawn up for our work, by Mr John Narien. 
Ifa square or rectangular area be covered with two 
vaults, penetrating each other at right angles, and form- 
ing two ridges which cross the area diagonally, and in- 
tersect each other at the common summit of the vaults, 
the arch thus formed is called a groined vault: the pe- 
netrating vaults may be either semicircular, or.semi- 
elliptical, or one of them may be semicircular, and the 
other semi-elliptical. The intersections of the circular 
3 
523 
or elliptical vaults, forming the ridges or groin angles, 
GRO ~a 
will be ellipses, because every oblique section of a cy- > 
linder or elliptical prism produces an elliptic curve, and — 
the case will be the same when one of the vaults is cir- 
cular and the other elliptical ; for if horizontal lines 
were drawn from points im the’ diameter or chord of the — 
circular vault perpendicularly to that diameter, and fis q 
ting in different points a lime drawn diagonally across ” 
the area, the ordinates drawn up to the ridge or groin 
angle from these points, will be respectively equal to _ 
the ordinates at the corresponding points under the cirs 
cular vault, and consequently their ends will be in the 
periphery of an ellipse. eiqtt 4 \ age 
The four vaults or arches forming the groined vault, 
spring from the angles of four square abutment piers, 
and if the intended vault is to be built of stone, the — 
courses in each arch respectively, are laid the cen- — 
tering in lines parallel to the axis of the arch they com. 
pose, in such a manner that the voussoirs of each arch 
meet the voussoirs of its adjacent arch at the groin | 
angle, where the faces of the angular voussoir in each 
course are wrought in such a manner as to form the — 
curve of the groin, which springs from the angle of a 
pier on which thearches stand. The upper surfaces of 
these angular voussoirs are also wrought, so that on both 
faces. they may coincide with the other stones of the 
same course, by which means these surfaces meet in a 
ridge which is always perpendicular to the curve of the. 
oin angle. When the intended yault is to be built of 
Brick, the internal faces of the brick voussoirs in each 
course are cut away at the groin angle, to receive the 
wedge-like end of a brick in the adjacent arch in the- 
same course, in order to bind the arches together E 
firmly: (See Fig. 1.) But as bricks have nelssliie Pr 
wrought stones, the form of a frustum of a wedge by cet: 
which they may sustain themselves when ied in Fig, 
the shape of an arch, their stability must upon 
the strength of the cement placed between them, which, 
uniting them into one mass, renders a structure of this 
kind a sort of vault hewn out of a rock. ‘ 
From a consideration of the above mentioned méde 
of constructing groined vaults, it will be evident that 
the pressures, both vertical and lateral, of all the arches 
of which they are composed, are resisted and sustained 
by the mutual intersections. of the courses of y 
at the groin angles ; these intersections may be consi- 
dered as squares upon the corners of the piers from. 
which they spring, the side of the square esne.aane) i 
to the thickness of the course of voussoirs, so that > 
diagonal ribs of the vault form as it were two arches,. 
which are kept ina state of equilibration, by the weight 
of the spandrils immediately over them, and serve as 
bases upon which the side arches with. their gto iy 
and all the superincumbent loading, UE ly ; 
hence it will be evident, that if the weight of the arches, 
with their loading over them, were in a constant ratio 
to the weight necessary for keeping the ribs in a state 
of equilibration, the whole vault would be in equilibrio __ 
in all its parts, This, however, cannot be attained in © 
practice, because the distances between the ribs at any 
Batt are never in proportion to the height of the span- 
rils, over the ribs at those parts, and therefore the 
groined vaulting will always in some degree be def ve 
i its equilibration ; besides the disadvantage arising firor 
he whole of the weight falling entirely upon the ribs, 
which receive no support from, the voussoirs of the 
contiguous side arches, whose joints are all oblique 
to the directions of the ribs. We = 
But as groined vaults are absolutely necessary in 
