. Asiatic Researches. m ON THE EARLY Chapter third. On measuring the breadth of rivers and the depth of wells, ist. Stand on the bank of the river, and through the two sights look at the opposite bank ; then turn round and look at any thing on the land side, keeping the astrolabe even. The distance from the observer to the object is the same as the breadth of the river, sd. Place something Chaucer's astrolabe had only one square, Dhil-i-As'bd, being divided into twelve The Umbra-recta is called Dhil-Mustawi, and the versa, Dhil-Mdcics, parts., The rule in the text is very inaccu- rately delive
. Asiatic Researches. m ON THE EARLY Chapter third. On measuring the breadth of rivers and the depth of wells, ist. Stand on the bank of the river, and through the two sights look at the opposite bank ; then turn round and look at any thing on the land side, keeping the astrolabe even. The distance from the observer to the object is the same as the breadth of the river, sd. Place something Chaucer's astrolabe had only one square, Dhil-i-As'bd, being divided into twelve The Umbra-recta is called Dhil-Mustawi, and the versa, Dhil-Mdcics, parts., The rule in the text is very inaccu- rately delivered; for the only case in which it will apply is when at the first station the index coincides with the dia- gonal of the square, and being afterwards moved one division on the horizontal side, the observer advances towards the object, till the top is again seen through the sights. For let A C be the height required, B the first station, D the se- cond;, As the angles at A and B are equal, A C = B C. But at the second position A C -. D Ca7 : 6. There- fore^ C==7 B D. But suppose at the first station JB, the index falls on the fourth division, Dhil- Kadam, on the,vertical side; and that, by retiring from the object to D^ it is brought on the third ; then it is evident that B CiAC:: 7:4, and DC t A C i: 7 : 3; Therefore DC = ^~ = 4 B D- Conseqxient" ly 7 :3°.*.&B D t AC. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Calcutta
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Keywords: ., bookcentury1800, bookdecade1810, bookpublishercalcu, bookyear1816
