The Art of projection and complete magic lantern ... - Yesterday Image

119is immersed, then as the water evaporates from beneath the thin glass,the threads will afford a continous supply, and the threads will notbecome dry until the whole of the liquid in the cup has become absorbedby them and evaporated.In this way we obtain the requisite conditionsfor continued growth of aquatic organisms. Care must be taken thatthe thin glass presses but slightly upon the object, another piece ofapparatus used for showing live objects is theFROGPLATE,which is a plate of stout brass about 6" long, fitting by means of adovetail piece into a female-fitting upon the stage, it is furnished with aglass disc let into one end flush, which is brought central to the openingof stage. To exhibit the circulation of blodd in the foot of a frog, one ofthe most beautiful and wonderful objects that is possible to be shownupon the screen ; take a full grow^n frog gently cleanse the animal fromany slime that may be about him and insert him in a small bag leavingone leg out, which secure by means of tying the mouth of bag, have readya number of pieces of soft silk which fix securely to each toe of frog andpass the other ends through the holes which will be found round theglass disc, this will leave the foot extended over the disc, now fix thebody of frog in bag which has been previously damped (let us make thething as comfortable as possible in its by no means enviable position) bymeans of a good long piece of tape carefully wound round the body, theend fixed by slipping under the spring on under side of plate, it is nowready to fix upon stage and show to the audience. It will be founda great advantage to gently smear the foot under observation with someglycerine, this prevents evaporation and a stoppage of the circulation,if so treated itcan be shown any length of time.THE POLARIZING APPARATUSConsists of two large Nicol's prisms and are composed each of twohalf-rhombs of calcareous spar, cemented together so as to transmit onlyone image.The polarizing apparatus is useful in bringing to light certainpeculiarities of structure which cannot be detected in any other way.The revolving selenite stage used in conjunction with tlie polarizingapparatus, consists of two selenites revolving by means of rack workwhich give by super-position the different waves of colour.The Klein's quartz and Iwave are used in the same subject and willbe found fully described under the heading of polarized light.