A Catechism of Familiar Things; Their History, and the Events Which Led to Their Discovery. With a Short Explanation of Some of the Principal Natural Phenomena. For the Use of Schools and Families. Enlarged and Revised Edition.

CHAPTER XIX.

AT­TRAC­TION, TIDES, GRAV­ITY, ARTE­SIAN WELLS, AIR, ANEROID BAROM­ETER, EAR-​TRUM­PET, STETHO­SCOPE, AU­DI­PHONE, TELE­PHONE, PHONO­GRAPH, MI­CRO­PHONE, MEGA­PHONE, TASIME­TER, BATH­OME­TER, ANEMOME­TER, CHRONOME­TER.

What is At­trac­tion?

By at­trac­tion is meant that prop­er­ty or qual­ity in the par­ti­cles of bod­ies which makes them tend to­ward each oth­er.

Are there sev­er­al kinds of at­trac­tion?

Yes. At­trac­tion has re­ceived dif­fer­ent names, ac­cord­ing to the cir­cum­stances un­der which it acts: The force which keeps the par­ti­cles of mat­ter to­geth­er to form bod­ies or mass­es, is called at­trac­tion of _co­he­sion_; that which makes bod­ies stick to­geth­er on­ly on their sur­faces, is called _ad­he­sion_; that which in­clines dif­fer­ent mass­es to­ward each oth­er, as the earth and the heav­en­ly bod­ies, is called _grav­ita­tion_; that which forces the par­ti­cles of sub­stances of dif­fer­ent kinds to unite, is known un­der the name of _chem­ical at­trac­tion_; that which caus­es the nee­dle of the com­pass to point con­stant­ly to­ward the poles of the earth, is _mag­net­ic at­trac­tion_; that which is ex­cit­ed by fric­tion in cer­tain sub­stances, is known as _elec­tri­cal at­trac­tion_.

How do you know that at­trac­tion ex­ists through the whole uni­verse?

This great uni­ver­sal law was first dis­cov­ered by Sir Isaac New­ton. The sun and plan­ets and oth­er heav­en­ly bod­ies are on­ly guid­ed in their path by grav­ita­tion.

Do we ex­pe­ri­ence this at­trac­tion up­on our earth?

Yes; be­cause our earth is car­ried around the sun by it; and, fur­ther, the tides show it very clear­ly.

What are the Tides?

The ebbing and flow­ing of the sea, which reg­ular­ly takes place twice in twen­ty-​four hours. The cause of the tides is the at­trac­tion of the sun, but chiefly of the moon, act­ing on the wa­ters of the ocean.

What is Grav­ity?

Grav­ity is the at­trac­tion be­tween the earth and the bod­ies on the earth, which makes what we call weight of bod­ies.

What do you un­der­stand by spe­cif­ic weight or grav­ity?

It means the weight of a body as com­pared with the weight of an equal bulk of some oth­er body tak­en as a stan­dard--com­mon­ly wa­ter.

Why do we say that cer­tain met­als--as, for ex­am­ple, plati­na or gold--are heav­ier than oth­ers, say, lead or iron?

Be­cause the for­mer have a greater spe­cif­ic grav­ity.

But is not a pound of gold as heavy as a pound of lead?

Yes; but a lump of gold will be heav­ier than a lump of lead of equal bulk.

Can we ex­plain by this what we call float­ing?

A body will float in wa­ter if its grav­ity is less than that of wa­ter; for ex­am­ple, wood floats for this rea­son in wa­ter, and a bal­loon in the air.

Why does a por­tion of the float­ing body sink be­low the sur­face of the wa­ter?

Be­cause the body in or­der to float must dis­place a por­tion of wa­ter equal in weight to the whole float­ing body.

But why do iron steam­ers float--iron be­ing heav­ier than wa­ter?

Be­cause the steam­er is not a sol­id piece of iron, but is hol­low, and so in­creased in bulk; for that rea­son the weight of the ves­sel and its con­tents is less than that of an equal bulk of wa­ter.

How can you as­cer­tain that air has weight?

We can do it by the barom­eter and by very many ex­pe­ri­ences in dai­ly life. If one end of a straw be dipped in­to a ves­sel of wa­ter and the oth­er end be sucked, the liq­uid will rise to the mouth. There we see the pres­sure of the out­side air forces the liq­uid through the straw where the air was re­moved by suck­ing.

Can you show the same by an­oth­er in­stru­ment?

Yes; the com­mon wa­ter pump demon­strates the same as the straw. A tube is placed in­to the wa­ter, the air is sucked out from the tube by the move­ment of the pump, and the out­side air press­es the wa­ter through the tube.

What are Arte­sian wells?

Wells so named be­cause they were made first at Ar­tois, in France. They work on the prin­ci­ple that ev­ery liq­uid seeks its lev­el. Of the rain which falls, a part soaks in­to the soil of moun­tains, un­til, com­ing to a lay­er of rocks or clay through which it can­not pass, it will col­lect and be stored up. If a hole be bored in­to this reser­voir the wa­ter will rise in it.

Do you know some oth­er prop­er­ties of air?

It is the most nec­es­sary sub­stance for our life; it is the ve­hi­cle of all odors and smells; it is the medi­um of all sounds, and brings to our ear and so to our mind an im­mense knowl­edge of the out­side world; it is the cause of the beau­ty of the blue fir­ma­ment or sky, of the au­ro­ra and twi­light; it is the great nurse of the whole veg­etable king­dom by clouds, rain, and dew.

What is an Aneroid Barom­eter?

It is a barom­eter in the con­struc­tion of which no quick­sil­ver or oth­er liq­uid is used. It con­sists of a met­al box, ex­haust­ed of air, the top of which is of thin met­al, so elas­tic that it read­ily yields to al­ter­ations in the pres­sure of the at­mo­sphere. When the pres­sure in­creas­es, the top is pressed in­wards; when, on the con­trary, it de­creas­es, the elas­tic­ity of the lid, aid­ed by a spring, tends to move it in the op­po­site di­rec­tion. These mo­tions are trans­mit­ted by del­icate levers to an in­dex which moves on a scale. This barom­eter has the ad­van­tage of be­ing portable.

What is the Ear-​trum­pet?

A trum­pet-​like in­stru­ment used to aid deaf per­sons in hear­ing. Its form is con­ical, and the larg­er end is of a bell shape; the small end is placed in the ear, and the per­son talks in the large end. It acts by con­cen­trat­ing the voice on the lis­ten­er's ear.

What is a Stetho­scope?

An in­stru­ment used by physi­cians for as­cer­tain­ing the ac­tion of the lungs, judg­ing by the sound of their mo­tion whether they are healthy or not.

De­scribe the Au­di­phone.

It is a fan-​shaped in­stru­ment to help deaf peo­ple, and is made of flex­ible car­bonized rub­ber. Fine silk cords at­tached to the up­per edge bend it over, and are fas­tened by a wedge in a han­dle. The top edge of this fan rests up­on the up­per teeth, and the sound waves strike its sur­face; the vi­bra­tions are thus con­veyed by the teeth and the bones of the face to the acous­tic nerve in the ear.

De­scribe the Tele­phone.

It is an in­stru­ment by which con­ver­sa­tion may be car­ried on at a dis­tance, and is com­posed of three parts--a thin disk of soft met­al, a small coil or bob­bin of silk-​cov­ered cop­per wire, and a small bar mag­net about four inch­es long. The bob­bin is placed on one pole of the mag­net, so that the wire is as it were steeped in the mag­net­ic space round the pole. The met­al disk is placed face close to the pole and bob­bin, so that when it vi­brates in front of the pole a se­ries of wave cur­rents will be set up in the coil of wire on the bob­bin. The whole is en­cased in wood, and a mouth-​piece is pro­vid­ed for speak­ing against the disk. The coil of wire on the bob­bin is of course con­nect­ed by its two ends in­to the cir­cuit of a tele­graph line.

Who in­vent­ed the Tele­phone?

It was in­vent­ed, al­most si­mul­ta­ne­ous­ly, by Alex. Gra­ham Bell, a na­tive of Scot­land, and Pro­fes­sor of Vo­cal Phys­iol­ogy in the Boston Uni­ver­si­ty, and El­isha Gray, of Chica­go.

What is a Phono­graph?

It is an in­stru­ment for record­ing the vi­bra­tions of sounds, and con­sists of a re­volv­ing cylin­der cov­ered with tin-​foil. To this cylin­der is at­tached a mouth-​piece, fit­ted with a thin plate or disk, on the out­er side of which, next to the cylin­der, is a nee­dle or point. The cylin­der runs on a screw, so that the whole length of it, from end to end, may pass un­der the point. On speak­ing in­to the mouth-​piece the voice caus­es the disk to vi­brate, and the point to trace marks cor­re­spond­ing to these vi­bra­tions on the tin-​foil. By turn­ing the cylin­der so that the point again pass­es in­to the marks in the tin-​foil, the sounds that en­tered at the mouth-​piece can be re­pro­duced at any time.

By whom was the phono­graph in­vent­ed?

By Thomas A. Edi­son, who was born in Ohio in 1847. Mr. Edi­son is the in­ven­tor of many im­prove­ments in teleg­ra­phy, which have been adopt­ed in­to gen­er­al use, and are to him the source of a large in­come. To him, al­so, we are in­debt­ed for the mega­phone, mi­cro­phone, tasime­ter, an im­prove­ment in the tele­phone, a sys­tem of elec­tric light­ing, and many oth­er in­ven­tions.

What is a Mi­cro­phone?

This in­stru­ment is a va­ri­ety of tele­phone by means of which faint sounds can be heard at a very great dis­tance. It con­sists of a small bat­tery for gen­er­at­ing a weak cur­rent of elec­tric­ity, a tele­phone for the re­ceiv­ing in­stru­ment, and a speak­ing or trans­mit­ting in­stru­ment. The last is a small rod of gas car­bon with the ends set loose­ly in blocks of the same ma­te­ri­al. The blocks are at­tached to an up­right sup­port, glued in­to a wood­en base board. This in­stru­ment is con­nect­ed with the bat­tery and the tele­phone. So won­der­ful­ly sen­si­tive is it, that the tick­ing of a watch, the walk­ing of a fly across a board, or the brush of a camel's-​hair pen­cil can be heard even though it be hun­dreds of miles dis­tant.

Will you de­scribe the Mega­phone?

It is a sub­sti­tute for the ear and speak­ing trum­pet. It con­sists of three pa­per fun­nels placed side by side. The two larg­er ones are about 6 feet 8 inch­es long and 27-1/2 inch­es in di­am­eter, and are each pro­vid­ed with a flex­ible tube, the ends of which are held to the ear. The cen­tre fun­nel, which is used as a speak­ing-​trum­pet, does not dif­fer ma­te­ri­al­ly from an or­di­nary trum­pet, ex­cept that it is larg­er and has a larg­er bell mouth. Two per­sons, each pro­vid­ed with a mega­phone, can, with­out oth­er ap­pa­ra­tus, car­ry on a con­ver­sa­tion at a dis­tance of one and a half or two miles.

What is the Tasime­ter?

It is an in­stru­ment, sen­si­tive to the small­est de­gree of heat, and is most­ly used in as­tron­omy. At­tached to a tele­scope it will show the heat com­ing from the stars.

What is a Bath­ome­ter?

This in­ge­nious in­stru­ment, the in­ven­tion of Prof. Siemens of Lon­don, en­ables those on board of ships to read from an in­dex the depths of the ocean be­neath them. It con­sists of a high­ly sen­si­tive steel spring to which a heavy piece of met­al is at­tached. The changes in weight to which the lat­ter is sub­ject in con­se­quence of the vari­ations of at­trac­tive force (the deep­er the ocean the small­er the lat­ter, and vice ver­sa) are reg­is­tered on a scale by the in­di­ca­tor that is in con­nec­tion with the steel spring.

What is an Anemome­ter?

An in­stru­ment for mea­sur­ing the ve­loc­ity and force of the wind, and by which storms, at a dis­tance, can be pre­dict­ed.

What is a Chronome­ter?

A time-​piece of del­icate and ex­act con­struc­tion, chiefly em­ployed by as­tronomers and nav­iga­tors. It dif­fers on­ly from an or­di­nary watch in its del­icate springs, in not be­ing so much in­flu­enced by heat and cold, and con­se­quent­ly in its ac­cu­ra­cy in giv­ing the time.