valleys, fail to excite the curiosity of a primitive people. It has been remarked by Laplace that even in his day the rising of Venus in its brightest phase never failed to excite surprise and interest. So there is little doubt that the first germ of science arose in the attention given by Eastern people to the changes of the moon and the motions of the planets. Perhaps the earliest astronomical discovery consisted in proving the identity of the morning and evening stars, on the grounds of their similarity of aspect and invariable alternation.14 Periodical changes of a somewhat complicated kind must have been understood by the Chaldeans, because they were aware of the cycle of 6585 days or 19 years which brings round the new and full moon upon the same days, hours, and even minutes of the year. The earliest efforts of scientific prophecy were founded upon this knowledge, and if at present we cannot help wondering at the precise anticipations of the nautical almanack, we may imagine the wonder excited by such predictions in early times.
Cambios Periódicos Combinados.
Rara vez encontraremos un cuerpo sujeto a una sola variación periódica y libre de otras perturbaciones. Podemos esperar que la variación periódica misma experimente cambios, que posiblemente sean seculares, pero que con mayor probabilidad resultarán ser periódicos; ni hay límite alguno para la complicación de periodos más allá de periodos, o periodos dentro de periodos, que en última instancia puedan revelarse.
Al estudiar un fenómeno de carácter rítmico, tenemos una sucesión de preguntas que hacer.
- ¿Es uniforme la variación periódica?
- Si no lo es, ¿es uniforme el cambio?
- Si no lo es, ¿es el cambio mismo periódico?
- ¿Es ese nuevo periodo uniforme, o está sujeto a algún otro cambio, o no?
y así sucesivamente ad infinitum.
En