s us with an elaborate toy； consisting of a group of birds which alternately whistle or are silent； while an owl seated on a neighboring perch turns towards the birds when their song begins and away from them when it ends。 The 〃singing〃 of the birds； it must be explained； is produced by the expulsion of air through tiny tubes passing up through their throats from a tank below。 The owl is made to turn by a mechanism similar to that which manipulates the temple doors。 The pressure is supplied merely by a stream of running water； and the periodical silence of the birds is due to the fact that this pressure is relieved through the automatic siphoning off of the water when it reaches a certain height。 The action of the siphon； it may be added； is correctly explained by Hero as due to the greater weight of the water in the longer arm of the bent tube。 As before mentioned； the siphon is repeatedly used in these mechanisms of Hero。 The diagram will make clear the exact application of it in the present most ingenious mechanism。 We may add that the principle of the whistle was a favorite one of Hero。 By the aid of a similar mechanism he brought about the blowing of trumpets when the temple doors were opened； a phenomenon which must greatly have enhanced the mystification。 It is possible that this principle was utilized also in connection with statues to produce seemingly supernatural effects。 This may be the explanation of the tradition of the speaking statue in the temple of Ammon at Thebes。 ｛illustration caption = DEVICE FOR CAUSING THE DOORS OF THE TEMPLE TO OPEN WHEN THE FIRE ON THE ALTAR IS LIGHTED （Air heated in the altar F drives water from the closed receptacle H through the tube KL into the bucket M； which descends through gravity； thus opening the doors。 When the altar cools； the air contracts； the water is sucked from the bucket； and the weight and pulley close the doors。）｝ ｛illustration caption = THE STEAM…ENGINE OF HERO （The steam generated in the receptacle AB passes through the tube EF into the globe； and escapes through the bent tubes H and K； causing the globe to rotate on the axis LG。）｝
The utilization of the properties of compressed air was not confined； however； exclusively to mere toys； or to produce miraculous effects。 The same principle was applied to a practical fire…engine； worked by levers and force…pumps； an apparatus； in short； altogether similar to that still in use in rural districts。 A slightly different application of the motive power of expanding air is furnished in a very curious toy called 〃the dancing figures。〃 In this； air heated in a retort like a miniature altar is allowed to escape through the sides of two pairs of revolving arms precisely like those of the ordinary revolving fountain with which we are accustomed to water our lawns； the revolving arms being attached to a plane on which several pairs of statuettes representing dancers are placed； An even more interesting application of this principle of setting a wheel in motion is furnished in a mechanism which must be considered the earliest of steam…engines。 Here； as the name implies； the gas supplying the motive power is actually steam。 The apparatus made to revolve is a globe connected with the steam…retort by a tube which serves as one of its axes； the steam escaping from the globe through two bent tubes placed at either end of an equatorial diameter。 It does not appear that Hero had any thought of making practical use of this steam… engine。 It was merely a curious toynothing more。 Yet had not the age that succeeded that of Hero been one in which inventive genius was dormant； some one must soon have hit upon the idea that this steam… engine might be improved and made to serve a useful purpose。 As the case stands； however； there was no advance made upon the steam motor of Hero for almost two thousand years。 And； indeed； when the practical application of steam was made； towards the close of the eighteenth century； it was made probably quite without reference to the experiment of Hero； though knowledge of his toy may perhaps have given a clew to Watt or his predecessors。
｛illustration caption = THE SLOT…MACHINE OF HERO （The coin introduced at A falls on the lever R； and by its weight opens the valve S； permitting the liquid to escape through the invisible tube LM。 As the lever tips； the coin slides off and the valve closes。 The liquid in tank must of course be kept above F。）｝ In recent times there has been a tendency to give to this steam…engine of Hero something more than full meed of appreciation。 To be sure； it marked a most important principle in the conception that steam might be used as a motive power； but； except in the demonstration of this principle； the mechanism of Hero was much too primitive to be of any importance。 But there is one mechanism described by Hero which was a most explicit anticipation of a device； which presumably soon went out of use； and which was not reinvented until towards the close of the nineteenth century。 This was a device which has become familiar in recent times as the penny…in…the…slot machine。 When towards the close of the nineteenth century some inventive craftsman hit upon the idea of an automatic machine to supply candy； a box of cigarettes； or a whiff of perfumery； he may or may not have borrowed his idea from the slot…machine of Hero； but in any event； instead of being an innovator he was really two thousand years behind the times； for the slot…machine of Hero is the precise prototype of these modern ones。 The particular function which the mechanism of Hero was destined to fulfil was the distribution of a jet of water； presumably used for sacramental purposes； which was given out automatically when a five… drachma coin was dropped into the slot at the top of the machine。 The internal mechanism of the machine was simple enough； consisting merely of a lever operating a valve which was opened by the weight of the coin dropping on the little shelf at the end of the lever； and which closed again when the coin slid off the shelf。 The illustration will show how simple this mechanism was。 Yet to the worshippers； who probably had entered the temple through doors miraculously opened； and who now witnessed this seemingly intelligent response of a machine； the result must have seemed mystifying enough； and； indeed； for us also； when we consider how relatively crude was the mechanical knowledge of the time； this must seem nothing less than marvellous。 As in imagination we walk up to the sacred tank； drop our drachma in the slot； and hold our hand for the spurt of holy…water； can we realize that this is the land of the Pharaohs； not England or America； that the kingdom of the Ptolemies is still at its height； that the republic of Rome is mistress of the world； that all Europe north of the Alps is inhabited solely by barbarians； that Cleopatra and Julius Caesar are yet unborn； that the Christian era has not yet begun？ Truly； it seems as if there could be no new thing under the sun。
X。 SCIENCE OF THE ROMAN PERIOD We have seen that the third century B。C。 was a time when Alexandrian science was at its height； but that the second century produced also in Hipparchus at least one investigator of the very first rank； though； to be sure； Hipparchus can be called an Alexandrian only by courtesy。 In the ensuing generations the Greek capital at the mouth of the Nile continued to hold its place as the centre of scientific and philosophical thought。 The kingdom of the Ptolemies still flourished with at least the outward appearances of its old…time glory； and a company of grammarians and commentators of no small merit could always be found in the service of the famous museum and library； but the whole aspect of world…history was rapidly changing。 Greece； after her brief day of political supremacy； was sinking rapidly into desuetude； and the hard…headed Roman in the West was making himself master everywhere。 While Hipparchus of Rhodes was in his prime； Corinth； the last stronghold of the main…land of Greece； had fallen before the prowess of the Roman； and the kingdom of the Ptolemies； though still nominally free； had begun to come within the sphere of Roman influence。 Just what share these political changes had in changing the aspect of Greek thought is a question regarding which difference of opinion might easily prevail； but there can be no question that； for one reason or another； the Alexandrian school as a creative centre went into a rapid decline at about the time of the Roman rise to world…power。 There are some distinguished names； but； as a general rule； the spirit of the times is reminiscent rather than creative； the workers tend to collate the researches of their predecessors rather than to make new and original researches for themselves。 Eratosthenes； the inventive world…measurer； was succeeded by Strabo； the industrious collator of facts； Aristarchus and Hipparchus； the originators of new astronomical methods； were succeeded by Ptolemy； the perfecter of their methods and the systematizer of their knowledge。 Meanwhile； in the West； Rome never became a true culture…centre。 The great genius of the Roman was political； the Augustan Age produced a few great historians and poets； but not a single great philosopher or creative devotee of science。 Cicero； Lucian； Seneca； Marcus Aurelius； give us at best a reflection of Greek philosophy。 Pliny； the one world…famous name in the scientific annals of Rome； can lay claim to no higher credit than that of a marvellously industrious collector of factsthe compiler of an encyclopaedia which contains not one creative touch。 All in all； then； this epoch of Roman domination is one that need detain the historian of science but a brief moment。 With the culmination of Greek effort in the so…called Hellenistic period we have seen ancient science at its climax。 The Roman period is but a time of transition； marking； as it were； a plateau on the slope between those earlier heights and the deep； dark valleys of the Middle Ages。 Yet we cannot quite disregard the efforts of such workers as those we have just named。 Let us take a more specific glance at their accomplishments。
STRABO THE GEOGRAPHER The earliest of these workers in point of time is Strabo。 This most famous of ancient geographers was born in