EECEEATIYE SCIENCE. 



165 



have already alluded to the four-cleft organ 

 of the willow herb, now look at the harebell 

 or campanula, and it is three-cleft ; find it 

 out in the grasses, and it is an elegant 

 feather ; in the primrose, a little knob like a 

 pin's head. 



We have already remarked that the 

 organs of the flower were essential and non- 

 essential with reference to the production of 

 seed, the essential being the stamen and 

 pistil. Nevertheless, the botanist regards 

 that blossom only which possesses all those 

 parts regularly developed as the type of a 

 perfect flower; a lychnis wanting in one 

 blossom the pistil, in another the stamens, 

 or the anemones with a petaloid calyx in- 



stead of corolla, are not perfect flowers, 

 botanically speaking. Be it remarked, too, 

 that not only must these parts be present, 

 but they must be developed in a regular 

 series of circles, or whorls, as they are called, 

 the organs alternating one with the other; 

 the coroUa divisions alternating with those 

 of the calyx, the stamens with the divisions 

 of the corolla on the one side, and with the 

 parts of the pistil on the other (Fig. 42) 

 These relative positions are, of course, altered 

 by variations in number and development, 

 but still they afibrd to botanists a standard 

 by which to judge in the determination of 

 doubtful parts. 



Spenceb Thomson, M.D. 



A POETABLE EQUATOEIAL. 



We may presume that every person who 

 can distinguish between the stars Sirius and 

 Polaris, knows what is meant by an equa- 

 toreal. However, as it is often well to place 

 the chief design or principle of a thing pro- 

 minently before the mind, when reference is 

 made to the details, we hope to be forgiven 

 if we begin at the beginning, and describe 

 the instrument as one by means of which a 

 telescope can be directed to any point in the 

 heavens ; and then, by the reading of two 

 graduated circles connected therewith, the 

 exact relation of that point in degrees, mi- 

 nutes, seconds, and fractional parts of seconds 

 to the pole, the first point of Aries, or to any 

 other point, can be ascertained with great 

 precision. 



Further, an equatorial of the first class 

 is so connected with clockwork, that the 

 telescope can by it be made to foUow a fixed 

 object above the horizon during the whole of 

 its apparent diurnal motion. 



Imagine a vertical shaft, with a telescope 

 attached to it, so as to allow the telescope 



to move at right angles to the shaft, on a 

 round axis in the shaft. By turning the 

 telescope, the complete tour of the horizon 

 can be made. Imagine a motion at right 

 angles to the former or parallel to the shaft, 

 and it is obvious that by these two motions 

 the telescope can be turned to any point 

 between the horizon and the zenith, if a 

 slight projection be made in the part con- 

 necting the telescope with the shaft, so that 

 the latter shall not interfere with the former, 

 when the instrument is nearly vertical. 



But this is not an equatorial. 



Now tilt the instrument, so that the at 

 present vertical shaft shall point to the pole, 

 or, in other words, be parallel to the axis of 

 the earth. The instrument becomes an equa- 

 torial. It may be the magnificent instru- 

 ment at Liverpool, probably, in mechanics, 

 the chef dJceuvre of the Astronomer Eoyal ; 

 at all events, tiU the erection of the very 

 recent one at Greenwich Observatory (see 

 Athenceum, June 11, 1859, p. 777) ; or it may 

 be our own plaything, the telescope belonging 



