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Article HISTORY OF THE ARTS AND SCIENCES FOR 1797. ← Page 2 of 3 →
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
History Of The Arts And Sciences For 1797.
when the moon is seen in a mean state of libration ; and where this boundary intersects the prime meridian at a ri ght angle , the two polar points of the moon are situated , of course each is at 90 de ° -, from the equator . Upon the stand of the instrument , designed to move this globe , is placed a brass hemisphere , on which the globe and all the parts are so fixed , as to have an easy and regular motion . The bar which
communicates to the globe all ttie motion from the other parts , enters it opposite to that point where the equator and prime meridian unite . - On its front are graduated semicircles , which determine the . quantity of motion given behind . When the globe is moved horizontally , it shews the libration in longitude . When moved by the pinion vertically , it exhibits the libration in latitude . On the edge of the brazen hemisphere are two marks-to note the pole of the ecliptic ; round which , by means of a wheel , the apparent motion of the moon ' s
polar axis revolves , both points of it being kept at the distance of z deg . 30 min . by means of a pin in the wheel , and placed out of its centre , whereby a peculiar motion is communicated to the globe . On the wheel are the signs of the zodiac , to shew the points of space to which the moon ' s polar axis is always directed ; and a moveable circle , on which are engraved divisions , respecting the periodical revolution of the moon , shewing when her revolution , with respect to
the ecliptic , as seen from the earth ' s centre , is accomplished . On this circle are also engraved the divisions of the moon ' s synodical revolution , by a continuation of the divisions , marking . the days and hours , & c . in a spiral direction under the former , to fill up the interval which is wanting between the accomplishment of the periodical and synodical revolution '; ' one index pointing to both . In the front a graduated meridian is fixed within the hemisphere ; to which are attached the above mentioned semicircles : one
representing the ecliptic , and at right angles to it another , named the terminator , -which ,- moving upon hinges , represents the boundary of light , in every state of the moon ' s elongation from the sun . ' . This is designed to shew what spots will appear in the plane of its illuminated hemisphere at any age of the mooii ; and in every degree of libration in latitude , longitude , and apparent polar obliquity . In
front of the lunar globe , at the bottom of . the brass hemisphere , is an arch , which supports " a small terrestrial globe , to familiarize the effects of the earth's parallax , or daily and monthly libration . For the convenience of observation , the terrestrial globe is made larger than the proportional angle which our globe subtends , as seen from the moon ; but converging lines upon a plane of brass , reduce it to its proper size , or to about two of the lunar degrees , at that end where this plate nearly unites to the large lunar globe . '
ACCOUNT OF Mil . CASH ' S INVENTION OF AN IRON BRIDGE . LETTERS Patent have been granted to Mr . John Nash , Architect , of Dover-street , London , for his invention of a new Iron Bridge ,
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
History Of The Arts And Sciences For 1797.
when the moon is seen in a mean state of libration ; and where this boundary intersects the prime meridian at a ri ght angle , the two polar points of the moon are situated , of course each is at 90 de ° -, from the equator . Upon the stand of the instrument , designed to move this globe , is placed a brass hemisphere , on which the globe and all the parts are so fixed , as to have an easy and regular motion . The bar which
communicates to the globe all ttie motion from the other parts , enters it opposite to that point where the equator and prime meridian unite . - On its front are graduated semicircles , which determine the . quantity of motion given behind . When the globe is moved horizontally , it shews the libration in longitude . When moved by the pinion vertically , it exhibits the libration in latitude . On the edge of the brazen hemisphere are two marks-to note the pole of the ecliptic ; round which , by means of a wheel , the apparent motion of the moon ' s
polar axis revolves , both points of it being kept at the distance of z deg . 30 min . by means of a pin in the wheel , and placed out of its centre , whereby a peculiar motion is communicated to the globe . On the wheel are the signs of the zodiac , to shew the points of space to which the moon ' s polar axis is always directed ; and a moveable circle , on which are engraved divisions , respecting the periodical revolution of the moon , shewing when her revolution , with respect to
the ecliptic , as seen from the earth ' s centre , is accomplished . On this circle are also engraved the divisions of the moon ' s synodical revolution , by a continuation of the divisions , marking . the days and hours , & c . in a spiral direction under the former , to fill up the interval which is wanting between the accomplishment of the periodical and synodical revolution '; ' one index pointing to both . In the front a graduated meridian is fixed within the hemisphere ; to which are attached the above mentioned semicircles : one
representing the ecliptic , and at right angles to it another , named the terminator , -which ,- moving upon hinges , represents the boundary of light , in every state of the moon ' s elongation from the sun . ' . This is designed to shew what spots will appear in the plane of its illuminated hemisphere at any age of the mooii ; and in every degree of libration in latitude , longitude , and apparent polar obliquity . In
front of the lunar globe , at the bottom of . the brass hemisphere , is an arch , which supports " a small terrestrial globe , to familiarize the effects of the earth's parallax , or daily and monthly libration . For the convenience of observation , the terrestrial globe is made larger than the proportional angle which our globe subtends , as seen from the moon ; but converging lines upon a plane of brass , reduce it to its proper size , or to about two of the lunar degrees , at that end where this plate nearly unites to the large lunar globe . '
ACCOUNT OF Mil . CASH ' S INVENTION OF AN IRON BRIDGE . LETTERS Patent have been granted to Mr . John Nash , Architect , of Dover-street , London , for his invention of a new Iron Bridge ,