OF A METEORIC FIRE-BALL. , 35 



ciled only by introducing changes in the elements of the orbit, one at the point just 

 named, and another near Lon. 74°. And it is worthy of note that, in the vicinity 

 of these points, observers report remarkable ruptures in the body of the meteor — 

 particularly at the former, where it separated into two parts that seemed nearly 

 equal in size, thus affording a rational explanation of the change in the elements. 

 The points of rupture are generally placed a few miles further east than I have 

 indicated, but it is allowable to suppose that two or three seconds may have inter- 

 vened after the rupture, before the parts became separated far enough to attract 

 attention. 



The first change in the elements, near the point of the chief explosion, became 

 evident early in the investigation, but great effort was used to avoid the necessity 

 of introducing the second. The most important phenomenon to be explained was, 

 that, while the meteor descended quite rapidly toward the earth till it reached the 

 meridian of about 74°, it afterward rose, and the change was too great to be 

 accounted for on the supposition that at that point it reached the perigee of its 

 hyperbolic orbit. The next most plausible explanation was that suggested by Prof. 

 Lyman in his article in the American Journal of Science and Arts, published shortly 

 after the meteor appeared, viz., that the change was due to the increased resistance 

 of the air, as the meteor descended into the denser portions of it. To test this 

 explanation, and, if possible, to deduce therefrom an orbit that would satisfy the 

 observations, I proceeded as follows, using data which, from the necessity of the 

 case, were in a good degree conjectural, so that the results, though correct in kind, 

 were only approximately so in amount. 



Starting with the fundamental equations 



7o(7. .24763, , „ v"- s' 

 Log. s' = — — y- h', and B = j~^ 1^ t 



in which s' represents the specific gravity of the air at the height h' above the sur- 

 face of the earth, d the diameter of a sphere moving through it, s its specific gravity, 

 V its velocity, p a constant quantity determined by experiment, and B the retar- 

 dation or loss in its velocity in the time t, it was necessary, in the first place to find 

 or assume probable values for d, s, and p. If we assume that the meteor when cold 

 was a sphere 100 feet in diameter, and having a specific gravity equal to that of 

 ordinary meteorites (3.54) ; but that it was expanded by the heat produced by the 

 condensation of the atmosphere till its diameter (d) was 500 feet, or 6000 inches, 

 the specific gravity (s) would then become .02832. The only experiment that I 

 could find, embracing aU the data requisite for determining the value of p, was one 

 at the Woolwich Arsenal in England, described in the article on " Gunnery" in the 

 Encyclopaedia Britannica, in which a bullet -^-^^ of an inch in diameter, and weigh- 

 ing 90 grains, was projected with a velocity of 2109 feet per second, and the 

 velocity lost in yi^- of ^ second was found to be 335 feet. The value of jj as deter- 

 mined by this experiment is 85.201. 



In applying the foregoing equations to the orbit of the meteor, it was assumed 

 that the retardation in a small arc of the orbit, 12 to 14 miles long, included between 

 two given values of co, was the same as though the meteor had been projected along 



