?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Huygens's+1688+Report+to+the+Directors+of+the+Dutch+East+India+Company+on+the+Measurement+of+Longitude+at+Sea+and+the+Evidence+it+Offered+Against+Universal+Gravity+&rft.creator=Schliesser%2C+Eric&rft.creator=Smith%2C+George+E.&rft.subject=History+of+Philosophy+of+Science&rft.subject=History+of+Science+Case+Studies&rft.description=When+Christiaan+Huygens+prepared+the+1686%2F1687+expedition+to+the+Cape+of+Good+Hope+on+which+his+pendulum+clocks+were+to+be+tested+for+their+usefulness+in+measuring+longitude+at+sea%2C+he+also+gave+instructions+to+Thomas+Helder+to+perform+experiments+with+the+seconds-pendulum.+This+was+prompted+by+Jean+Richer's+1672+finding+that+a+seconds-pendulum+is+1+1%2F4+lines+(2.8+mm)+shorter+in+Cayenne+than+in+Paris.+Unfortunately%2C+Helder+died+on+the+voy%C2%ACage%2C+and+no+data+from+the+seconds-pendulum+ever+reached+Huygens.+He+nevertheless+did+receive+data+from+his+clocks+on+the+return-voyage+from+the+Cape+of+Good+Hope+to+Texel.+When+he+first+calculated+the+ship's+course+according+to+these+data%2C+it+appeared+to+have+gone+straight+through+Ireland.+He+then+tried+introducing+a+correction+to+the+data%2C+based+on+an+idea+he+had+previously+entertained+as+a+possible+explanation+of+Richer's+finding%3A+he+corrected+the+observed+time+to+com%C2%ACpen%C2%ACsate+for+a+reduction+in+the+effect+of+gravity+from+the+Poles+to+the+Equator+resulting+purely+from+the+Earth's+rotation.+His+newly+calculated+course+convinced+him+that+this+rotational+effect+is+the+sole+source+of+any+variations+in+gravity+with+latitude.+This+paper+examines+Huygens's+correc%C2%ACtions+to+the+data+and+his+reasoning+from+the+new+course+to+the+conclusion+that+nothing+else+causes+a+variation+in+gravity.+In+the+process%2C+we+show+that+Huygens+had+cogent+empirical+reasons+to+reject+Isaac+Newton's+theory+of+universal+gravity%2C+which+predicted+a+some%C2%ACwhat+larger+variation+in+gravity.&rft.date=2000-01&rft.type=Preprint&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.identifier=http%3A%2F%2Fphilsci-archive.pitt.edu%2F5510%2F1%2Fgseric.pdf&rft.identifier=Schliesser%2C+Eric+and+Smith%2C+George+E.+(2000)+Huygens's+1688+Report+to+the+Directors+of+the+Dutch+East+India+Company+on+the+Measurement+of+Longitude+at+Sea+and+the+Evidence+it+Offered+Against+Universal+Gravity.+[Preprint]&rft.relation=http%3A%2F%2Fphilsci-archive.pitt.edu%2F5510%2