HEL 
stood. These sphinxes are, however, no, longer visible, 
my ate no doubt covered with the soil deposited by 
the Nile; and we agree with Dr Clarke in thinking, 
that not only the sphinxes, but even the pavement of 
the temple, might be disclosed by a very trifling exca- 
vation. 
The obelisk or pillar of On, which is now the only 
of antiquity that marks the site of Heliopolis, is 
i ee seeceine ts seve le. Ac» 
cording to Dr C ‘ke, who has given a very correct en- 
graving of it, it is one entire mass of ish granite. 
of its. four sides exhibits the same characters, and 
in the same order. Those which face the south have 
been the least affected by the decomposition of the sub- 
stance in which they are hewn; and it is from the 
southern side that Dr Clarke's ving is taken, For 
@ particular account of this reat ipa the hi ly- 
phics which it contains, the reader is referred- to Kir- 
‘cher Syntagma VIL. Theat. Hieroglyph. Gidipi 
tiaci, tom. iv.«p. 330; Pococke’s, Description of the 
East, vol. i, p. 23; Shaw’s Travels; Norden’s Travels; 
but. particularly Dr. Clarke's, Travels, -part ii, sect. ii. 
98.° 
a HELIOSTATE, or Hettostara, from nares the sun, 
and setnes I stand, is the name of a very ingenious and 
useful instrument, ‘invented by Dr s’Gravesande, who 
was professor of mathematics at Leyden. The object 
of it is to give such a-motion, by means of clockwork, 
to a polished mirror, that the beam of the sun which it 
reflects may be fixed, or remain in the same position du- 
ring the diurnal motion of the earth. Hence it is of 
great use in all optical experiments, in which it is re- 
quired to transmit'the solar rays into a dark room. 
The heliostate, which is represented in Plate CCXC. 
Fig. 1. consists of two principal parts; Ist, A plane 
metallic speculum; supported ‘bya stand; and, 2d, A 
clock for giving motion to the speculum. The specu- 
lum §, contained in a wooden frame, is placed in the 
brass case a, a, and is suspended by. the handle AA, so 
as to have a free “tae prep ov axis aa, which 
should along the surface o' speculum. The 
handle KA is joined to the cylinder C, whose axis: is 
coincident with the middle part of the axis aa of the 
um. The axis of the tail DF, joined: perpendi- 
cularly to the-hack of the speculum, is directed to the 
same point. This tail is made of a cylindrical brass 
wire, about the sixth part of aninch in diameter. The 
cylinder’C is put upon the wooden stand P, the upper 
part of which. is shewn tely in Fig, 2. The 
smooth iron cylinder e goes into a cavity in the copper 
cylinder C, sothat by the motion of the tail DE, the 
sition of the speculum may penennonairerent he 
wooden stand P is raised. and depr the three 
brass screws B, B, B, turned witha key, and moving in 
‘a plate of brass. 
The clock is represented at H, with an index which 
. revolves once in 24 hours. The plane of the clock is 
. inclined to the horizon, at-an angle equal to the co-la~ 
titude of the place. ». The copper pillar FG, which a 
ports. the. clock, consists of two parts, joined by 
screws d,d, between which, as in a sheath, is moved 
an iron plate, in the middle of which there is a slit 
through which..these screws pass. This plate is fixed 
21st March, ist March. 21st Feb. 11th Feb. 
2ist Sept. 11th Oct. 21st Oct. 1st Nov. 
, Parts, Parts. Parts. Parts. 
0 8 17 32 
VOL..X, PART. II, 
705 
HEL 
to the lower plate-of the ‘clock itself, so that it can be 
raised and depressed, and fastened at an 
screws d,d, ‘The same effect may also 
the screws I, I, I i ° 
L, og The paper 4’ c’ must be in the same 
straight line, and a verti ne passing through them 
must be perpendicular to the Ipalnenhalbatis Goma on 
the plane of the clock, such as,f‘g, hi. 
hen the plane of the clock is. inclined. at.an angle 
equal to the co-latitude of the place, the plane LLM 
must be brought into a horizontal position by the plum- 
met Q, the point of which is to coincide with a 
point 0, marked on the foot M. But if it were re- 
quired to use the instrument in another latitude, another 
point o would require to be. marked ; and it would be 
n to incline the plane LLM to the horizon. The 
axis of the wheel which moves the index has.a cylindri- 
cal perforation, but a little narrower below than above. 
The index, shewn separately at ON, in Fig. 3. is made 
of brass, and has a tail pg exactly filling the above 
mentioned perforation, into which it is thrust ti so 
as to stick'and be carried by the wheel. The 
tail pq has also a cylindrical hole, through which 
the small. brass wire /4, which remains in any 
—- into which it is put. At the end o of the in- 
ex there is a small cylinder n perforated cylindrically. 
The length of the index n n’ was six inches in s'Graves- 
ande’s machine. 
The iron tail ¢ (Fig. 
4.) of the piece T goes into the 
cavity n; Fig. 3, as 
ewn in Fig. 1. and moves in it 
Hehiostate, 
Pate 
coxe. 
Fig. 3. 
Fig. 4, 
freely, though not loosely. The small pipe R, Fig. 5. pig, 5. 
through which the tail DE of the speculum may be mo~ 
ved freely, may be suspended at different heights be- 
tween the legs of the piece T (Fig. 4.) the screw 
rr going into the parts mm of the pipe. The pipe can 
then turn freely round mm_as.an axis. “yr 
In order to fix the machine, another part, called the 
oo must’ be, used. The cylinder and the specu- 
m: being removed from the stand P, the brass pillar 
VX (Fig. 6.) is stuck tight upon e, Fig, 2. The ruler 
YZ moves round a centre at X, so as to remain in any 
position in which it is placed. The arm XZ has a 
jar construction and a. certain » but the 
ength of XY is determined at pleasure. The end Xy 
of the ruler, which does not extend beyond y, is in« 
ee a Nei RO po - 
site side. y are joined at Z, and are together 
Sucbenimmmbaheone Seeenmeen 
ed ruler Xy. On —— is er 
vs, whose is equal to 72. parts. length of 
the index. arm XZ is equal to the length of the 
index, reckoning from the centre of motion at X tothe 
end Z, when:x coincides with v, where the divisions en 
vs commence: The line vs, which is unequally di- 
vided, serves to determine the length of the arm XZ 
for different times of the year, by bringing 2 to the di« 
vision oe to the given day when the ma- 
chine is u 
In order to mark the divisions, the arm is supposed 
to be divided into 1000 parts, hence vs will be 90 
The distances corresponding to different times 
of the year, are set down in the following table. 
Ist Feb, 21st Jan. 11th Jan. 2lst Dec. 
11th Nov, 2lst Noy. 1st Dec, . 2ist Dec. 
Parts, Parts, Parts, Parts. 
47 64 77 90 
4uU 
Fig, 6 
