| Show GREAT telescopes why thy they are of more service to science than small instruments it is frankly to be admitted that for ordinary work enormous instruments are not advantageous those of moderato moderate dimensions will do far more easily and rapidly y the work for which they ire are capable it would be poor economy nr to shoot squirrels with fifteen inch cannon observers with smaller instrument ment if they have sharp eyes and use them faithfully can call always find enot enough irh to do and do it well but the great telescope has two advantages which are decisive in III the first place it collects more li light and so makes it possible to use higher in magnifying powers and thus virtually to draw lie nearer aber to the object studied th than in wo we can with the smaller one and in th the e next place in consequence of what is known as diffraction the imago image of a luminous point made by a largo large lens is smaller smalle r and sharper than that made bya by a small one the smaller the telescope the lar larger larer er are the so called spurious disks of a star so that in the else case of a close double star for instance where our nine inch telescope shows only an oval disk the twenty three inch shows two fine distinctly separated points it is true that the atmospheric disturbances which prevail toa to a greater or less extent very seriously affect the seeing 0 with large instruments the power of the prince of the air which is t toan ll 11 astronomer the very 0 afe type of the total depravity of an inanimate things 0 on nine clear nights out of ten deprives a great telescope of much of its just superiority so that on an ordinary ii I 1 glit a 0 good observer with an aperture of twelve or fifteen inches can make out all that can bo be fairly seen with twenty four or thirty inches at the same time and yet the writer has continually Teri verified fied in his experience the observation of mr dark clark who said you can always see with a large telescope every thill tiling 0 shown by a smaller one a little better if the scein seeing is bad immensely better if it is good but when a really ily good night comes as once bouce in a while it les does then to a great telescope heaven opens new worlds appear old illusions are dissipated and observations and measurements ure ments before beyond the reach of human skill become possible easy and accurate in fact the ot wanting still larger telescopes is identically the same as that of wanting a tel telescope atall a at tal all of course itis it is p 1111 impossible to predict what discoveries will be made with tha ali i great lick telescope when it is erected on its mountain of privilege 0 very likely none it is not possible now to go cut at night 0 as some seem to think and pick up discoveries as one would gather flowers in a forest but we maybe may be sure of this that it will collect data with micrometer camera and spectroscope which will remove many old difficulties will clear up doubts will actually advance our knowledge e and what is still more important will prepare the way and hew the steps for still higher climbing 0 toward the stars prof young in forum |
