ORRERY. 
Tassie of Fergufon’s bee said their correfponding 
Per in Tim 
fviotions. Wheelw rk. Periods. - 
D. H. M. S. 
Earth’s diurnal 7 {25 69 83 
motion - t 3 x - x 7 365 «65 48 58.78 
A lunation- 7 x 3 29 12 45 Oo 
: «| 25 69 64 
Sun’s rotation 3 x os 25 6 35 36 
Revol. of Venus 2 2 x a 22420 47 8 
Rev. of Mercury 
2 of Venus + 1] 87 23 47 24 
Rot. of Venus - 24 22 31 «8 
2 of its revol. 
74 
Moon’s node - 18% years, 
- Earth’s parallelifm 1 revolution. 
Befides thefe wheels and pinions there are others for fub- 
fidiary purpofes, which 
an appendage to Fergufon’s 
The pic aieeea by the author are 
as follow; viz 
D He M S&S 
Earth’s ove motion - - 365 5 48 57 
A lunatio - - 29 12 45 Oo 
Sun’s ree - - 25 6 90 0 
Revolution of Venus -  - 224 17° 0 0 
itto of Mercury - += - 87 23 0 Oo 
Rotation of Venus - - 24 8 0 Oo 
It may be faid in favour of this ftatement, that de. 
{cription is a popular one, aes therefore fufficiently ac- 
eurate for ordinary readers ; when the author under- 
takes to appreciate the errors oF his ema which he 
has done, a more correét report of the periods is indifpen- 
fable. e rotation of Venus, according to Bianchini’s 
determination, which Fergufon has here adopted, is no 
longer confidered as the tia) rotation. There is con- 
fiderable ingenuity fhew the contrivance for making 
the rotations of the andl ce with aps of the eee 
Mr. Benjamin Martin’s Orrery, or Microcofm.— 
fecond volume of ore ai Martin’s « Mathematical Toit. 
tutions’ 
that the plan was ever put into exe 
tended to be the regular sine heir of all the folar fyf- 
ould exhibit the planetarium portion in 
of the clock, the tellurian in stg and the 
one in . third; and, as it fhou a Jovian luna- 
um intended to be oceafionally fabtitated “for a 
planctarigm, . go by the motion of the clock, The 
aa however, after having propofed his plan, feems to 
ve defpaired of having any order given to make fuch a. 
pee of mec hanifm, chiefly from a confideration, which is 
equally true in our own time ; viz. that ‘ by arts and artifs 
we underftand only engraving, painting, and feulpture, and 
thofe who practife them ;”’ ntific mechanif{m being not 
ufually comprehended under thofe terms, as being but little 
cultivated ; and sack more rage fadics of chemiftr 
and galvan nifm m, we 
dern planetaria, tellurians, and lunaria, which conftitute the’ 
orrery in three parts, as conftructed by the. workmen of 
Meffrs. Adams, Jones, &c.; on which account we fhall 
defcribe the different portions feparately, and fuggeft fuch 
obfervations to the reader as may enable him 
ticle PLANETARIUM, where our plan of arrangement has 
placed it as a feparate inftrument. 
The Tellurian Portion.—Tellurian is a word which owes 
its origin, we believe, to B. Martin, and which implies a 
detached portion of mechanifm, calculated to reprefent the 
—_ and diurnal motions of our earth (tellus) only, and 
s fuch, was at firft, as it ftill continues to be, an appen- 
age to the seetanns and forming with it and the luna- 
rium the common orrery : the principal requifites for this 
rument, or rather portion of an inftrument, are a train 
of wheels: foe oes the conftant parallelifm of the 
earth’s axis, on which, together with its proper spear se 
depends the change of feafons, and another train compo 
of an exact ratio between a folar da 
i For the defirable purpofe of leffening the num- 
ber of wheels which would be required in two diftin& 
trains, the inventor has very acai fixed upon two 
wheels ars fhall b 
e common trains, viz. 365 
and 59; the former of thefe, which is neceffarily large, 
has no ee itfelf, but t communicates a circular motion 
to th 
8 whe e ig 
with it on the annual bar, will continue as 
long as the handle moves which a¢tuates the annual bar. 
The trains made choice of are thefe; viz. 
For the Earth’s pa-l 59 | _ 3658 
rallelifm  - 3 65 * lo 7 3 a RE hoeee 
= and we 59 10), 8 8 x 12 3654 of 0 
2 20 °° 40 re 
often as the ieee toa re- 
- f{pe& to the a train, the vane ‘of which oeht to have oir 
365.4% 
