‘Heliostate 
l] 
Helston. 
Method of 
using the 
instrument. 
PLATE 
ceoxe, 
Fig. 1. 
Fig, 7% 
Simple he- 
liostate pro- 
posed by 
Dr Young. 
Pate 
€cxec, 
Fig. 8. 
HEL 
given in the following Table. 
706 
On the opposite side of the ruler is drawn another line corresponding to vs, the 
HEL 
divisions for which are 
21st March. 11th April, 21st April. 1st May. 11th May, 21st May. Ist June. 21st June. 
21st Sept. 1st Sept. 2ist Aug. 11th Aug. Ist Aug. 21st July. 11th July, 2istJune. - 
Parts. Parts, Parts, Parts, Parts. Parts. Parts. \ Parts, *. 
0 11 22 36 51 66 79. 90 | , 
The instrument being thus constructed, is used in 
the following manner. Having adjusted the point x 
of the placer to the division for the day of the month, 
place XV upon the stand P, and put the ruler Y into 
the position and direction in which it is wished to fix 
the solar ray. The lines dc, ’c’ are placed in a meridian 
line drawn on the plane, and the point of the plummet 
Q is brought too. The index NO is then turned till 
the sun’s rays pass directly through the pipe R, which 
may be varied in its ‘position till this is effected. The 
brass wire J is then raised or depressed till the shadow 
of the end of it / passes through the middle of the pipe 
R. This part of the machine is then moved to the 
placer as formerly adjusted ; but the clock is moved and 
raised in such a manner that the end / of the brass 
wire / may coincide with the end Z of the ruler YZ. 
The sun’s rays, and the shadow of / passing through R, 
and the point of the plummet corresponding with 0 ; 
the pillar VX with its ruler is removed, ‘and the cylin- 
der C, carrying the speculum §S, is substituted in its 
place, without altering the position of the stand P. The 
piece T is taken ont of its place, that the tail DE of 
the speculum may be put through the pipe R; and when 
the piece T is replaced, the machine is then ready for 
use. The rays reflected from the speculum have the 
same position and direction as the ruler of the placer ; 
and while the tail of the speculum moves with the 
clock, whose index follows the sun, its situation is al- 
tered with respect to the sun, but the ray reflected from 
the centre of the speculum remains fixed. By substi- 
tuting the index K, Fig. 7. in place of NO, the ma- 
chine becomes a common clock. For a demonstration 
of the truth of the preceding construction, the reader is 
referred to s’Gravesande’s Physices Elementa Mathe- 
matica, tom. ii. p. 714. 
A very simple substitute for the heliostate, as pro- 
posed by Dr Thomas Young, is shewn in Fig. 8. A 
mirror C is fixed on the outside of a window facing the 
south, opposite the aperture D, through which it is 
required to transmit the solar rays. Another mirror is 
fixed by a joint to a rod AB, moveable about its axis, 
and parallel to the wxis of the earth. The mirror A 
being placed in a position required for the day, so that 
the light which it reflects is received at such an angle 
upon C, that it may be transmitted through the aper- 
ture. In order to keep the ray in this position, nothing 
more is necessary than to turn the axis BA round on its 
socket. See Young’s Nat. Phil. vol. i. p. 426,785. An- 
alogous contrivances by Peyra¥d will be found in the 
Phil. Magazine, vol. xxxvii. p. 183, &c: 
HELIOTROPIUM. See Mineratoey. 
HELIX. ‘See Concnotoey, vol. vii. p. 79, 
HELLESPONT. See Turkey. 
HELMINTHOLOGY, is a term in zoology, derived 
from sAyive, an earth-worm, and roves, a discourse, Un- 
der this head are included those animals which Lin- 
neus called vermes. For an account of the different 
orders of this class, see. ANIMALCULE, ConcnoLoey, 
Inrestina, Motiusca, Rapiara, and Zoornytes. 
HELOISE, See Aperarp, vol. i: 
HELSTON, a town of England in the county of'Corn- 
wall, is situated on the side of a hill, which slopes gently 
to the little river Cober, The town consists principally 
of four streets, which meet in a centre, and form. a cross, 
and a channel of water runs through each of them. 
The market-house and town-hall stand near the middle 
of the principal street. The church, which was erected 
in 1762 on an eminence to the north, has a pinnacled 
tower 90 feet high, which forms a conspicuous sea 
mark. There was formerly a priory and a strong 
castle at Helston. Some vestiges of the castle were 
seen in the time of Leland. The priory of the knights 
of St John of Jerusalem was at St John’s village, near 
the town. The remains of it were destroyed some 
years ago to make room fora Methodist meeting-house. 
The town is governed by a mayor, five aldermen, a 
recorder, and sworn freemen, amounting to 36. Hel- 
ston was one of the original stannary towns, but 
little tin is now stamped here. Vessels take in: their 
lading at a good harbour, a little below the town. Near 
Helston is a curious heap of stones, piled up in the 
form of a circle. It is called Earth Castle, and was for- 
merly used as a fortification. 
The population of the burgh and parish, in 1811, 
was, 
Number of inhabited houses. 
I Ey 1 Se 
Number of families . . . ... 531 
Ditto employed in agriculture . . . 119. 
Ditto in aa A and manufactures . + 166- 
Males . Biiacbinas busi noe otha als oe 
EIBRIES. Fin ae aus 8 then O4.4u. 8 | ae 
Total populationin 1811. . .. . 2297 
, Pies 
See the Beauties of England and Wales, vol. ii. p. 
455. 
HELVETIA. See Switzervanp. 
HELVETIUS, Craupre Aprian, a celebrated me- 
taphysician, of the modern school, was born at Paris in 
January 1715. His ancestors, originally of the Palati- 
nate, had been obliged, by their attachment to Protestant 
principles, to remove to Holland. His father, grand- 
father, and great grandfather belonged to the medical 
profession, and were all men of eminence. His grand~ 
father in particular obtained celebrity by the introduec- 
tion of ipecacuanha into the Materia Medica. M. Hel-« 
vetius, the father of the subject: of this article. was 
physician to the Queen of France, and held in great ho~ 
nour. at coprt, was’ well known through Europe as a 
man of talents, and highly esteemed by all who knew - 
him, for the probity of his character. gave his son 
an excellent education, by placing him very early under 
the care of an intelligent tutor, M. Lambert. The 
young Helvetius was remarkably docile, and rapidly 
imbibed the spirit of the different authors whom he 
read; and from his exquisite sensibility to praise, he 
rendered himself an early proficient in literature, dan- 
cing, fencing, and the various other accomplishments 
which produce admiration. At: college he became 
warmly attached to the philosophy of Locke. To trace 
all mental operations to sensation, appeared to him a 
happy explanation of these. complicated phenomena ; 
and he became animated with an ambitious desire to 
improve and extend the principles which he so much 
admired. At the age of twenty-three, he obtained the 
very lucrative situation of a farmer-general, He in-. 
