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Article THE CHEMISTRY OF COMMON THINGS. ← Page 4 of 7 →
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The Chemistry Of Common Things.
should be a separate portion , forming , as it were , a pane of glass of itself The practice of painting the lower portions of plate glass windows of a dark blue or green colour is now becoming very prevalent . The subject is one of great importance , on account of the costliness of large sheets of plate glass . " It Is believed that those which formed the window of the Greenock offices of the Magnetic Telegraph Company
must have cost £ 50 to £ 60 . It is probable that there is more truth n the idea that a feeling of warmth is suggested by the colour red—• an effect which is generally ascribed to its similitude to the colour of fire , but which may likewise be attributed to a small quantity of heat being thrown off with the red ia ^ tion , so slight , however , as not to be distinctly perceptible .
These instances of the rIStion of heat to- colour seem to point to a quality among the rays of the spectrum analogous to that of the specific heat of ponderable bodies—bodies of different colours being differently affected by the same degree of radiation . The specific heat ,
if we may so apply the term , of coloured rays , and consequently their heating power , varies with their refrangibility . The heating power of the rays absorbed by a coloured body determines its absorbing power —that of the reflected rays , its reflecting and radiating powers .
These facts are sufficient to show the intimate connection which exists between light and heat , and we should have no hesitation in pronouncing heat to be merely a quality of light , or light of heat , but for instances in which light and heat appear to exist apart from and independent of each other . In the first place , bodies when heated do
not emit any sensible amount of light until their temperature is raised to about 800 ° , and in the phosphorescence of certain substances no heat can be discovered . But perhaps the most remarkable instance of light unaccompanied by heat is in the case of the moon . De La Hire and others collected the rays of the full moon in powerful burning glasses , yet they had no effect upon delicate thermometers placed
in their foci . But if these instances are objections to the hypothesis of the identity of light and heat , they do not entirely disprove it . Bodies may probably emit light at temperatures below that at which they become sensibly incandescent , but in so slight a degree as not to be capable of affecting the sight ; and in the case of Be La Hire ' s experiment , as the light of the moon is calculated to be less than 1 * 300 , 000 th part of that of the sun , the thermometer would not , if the heat be supposed to follow the same proportions , be affected to the extent of one-twentieth
of a degree . 5 . / Sources of Heat . —The principal sources of heat may be classed under six divisions : — solar light ; chemical action ; conduction of vapours and solidification of liquids ; friction , percussion , and compression ; animal life ; electricity . Hie earth receives heat from the sun by radiation , in the same banner as a cold body receives heat from a heated one placed at a
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things.
should be a separate portion , forming , as it were , a pane of glass of itself The practice of painting the lower portions of plate glass windows of a dark blue or green colour is now becoming very prevalent . The subject is one of great importance , on account of the costliness of large sheets of plate glass . " It Is believed that those which formed the window of the Greenock offices of the Magnetic Telegraph Company
must have cost £ 50 to £ 60 . It is probable that there is more truth n the idea that a feeling of warmth is suggested by the colour red—• an effect which is generally ascribed to its similitude to the colour of fire , but which may likewise be attributed to a small quantity of heat being thrown off with the red ia ^ tion , so slight , however , as not to be distinctly perceptible .
These instances of the rIStion of heat to- colour seem to point to a quality among the rays of the spectrum analogous to that of the specific heat of ponderable bodies—bodies of different colours being differently affected by the same degree of radiation . The specific heat ,
if we may so apply the term , of coloured rays , and consequently their heating power , varies with their refrangibility . The heating power of the rays absorbed by a coloured body determines its absorbing power —that of the reflected rays , its reflecting and radiating powers .
These facts are sufficient to show the intimate connection which exists between light and heat , and we should have no hesitation in pronouncing heat to be merely a quality of light , or light of heat , but for instances in which light and heat appear to exist apart from and independent of each other . In the first place , bodies when heated do
not emit any sensible amount of light until their temperature is raised to about 800 ° , and in the phosphorescence of certain substances no heat can be discovered . But perhaps the most remarkable instance of light unaccompanied by heat is in the case of the moon . De La Hire and others collected the rays of the full moon in powerful burning glasses , yet they had no effect upon delicate thermometers placed
in their foci . But if these instances are objections to the hypothesis of the identity of light and heat , they do not entirely disprove it . Bodies may probably emit light at temperatures below that at which they become sensibly incandescent , but in so slight a degree as not to be capable of affecting the sight ; and in the case of Be La Hire ' s experiment , as the light of the moon is calculated to be less than 1 * 300 , 000 th part of that of the sun , the thermometer would not , if the heat be supposed to follow the same proportions , be affected to the extent of one-twentieth
of a degree . 5 . / Sources of Heat . —The principal sources of heat may be classed under six divisions : — solar light ; chemical action ; conduction of vapours and solidification of liquids ; friction , percussion , and compression ; animal life ; electricity . Hie earth receives heat from the sun by radiation , in the same banner as a cold body receives heat from a heated one placed at a