JiLY 1, 1897.] 



KNOWLEDGE. 



159 



is not only not dark, bat is, on the contrary, absolutely 

 palpitating with light, though there be light which our 

 eyes may never see, and sounds which our ears may never 

 hear. But science has not yet pronounced its last word 

 on the hearing of that which is inaudible, and the seeing 

 of that which is invisible." Finality, indeed ! When you 

 put on the armour of science you begin a warfare in which 

 the individual enemy has the tantalizing knack of resolving 

 itself into a plurality of foes ; you feel as if you were 

 walking out from a gently sloping beach into the sea, 

 sometimes sinking suddenly over head in holes you didn't 

 expect to find, and finally you find yourself floundering 

 hopelessly in the unfathomable depths of the unknown. 



Prof. Lockyer, referring to the unexplored domains of 

 science, was once overheard to say : " Ah, my friend, 

 science is not yet born ; it is only conceived." 



It is true that man has arrogated to himself the 

 sovereign epithet, " Lord of Creation," and with some 

 claim to the distinction ; but from the remotest antiquity, 

 through all the vistas of the ages up to the present time, 

 the birds and insects and other denizens of the air have 

 been, as it were, trying to teach us to fly. We have at 

 last fully realized the fact that our position in the cosmos 

 is fixed— our migrations limited to the skin of the planet 

 on which we live and to a thin film of air which surrounds 

 it. Habit has not dolled the edge of wonder, and we may 

 live to see air ships a common sight. Prof. Langley says : 

 " A flying machine, so long a type for ridicule, has really 

 flown ; it has demonstrated its practicability in the only 

 satisfactory way — by actually flying, and by doing this 

 again and again under conditions which leave no doubt. . . . 

 The world, indeed, will be supine if it do not realize that 

 a new possibility has come to it, and that the great 

 universal highway overhead is now soon to be opened." 



Our obligations to the old astronomy find their expression 

 in the navigation of the seas, the calculation of the tides, 

 and the daOy regulation of time. What of the new 

 astronomy? Can we derive material assistance from her 

 in the routine of daily life ? Dr. Huggins happily eluci- 

 dates this point in the following words : " Her sphere 

 lies outside the earth. Is she less fair ? Shall we pay 

 her less court beciuse it is to mental culture in its highest 

 form, to our purely intellectual joys, that she contributes ? 

 For surely in no part of nature are the noblest and most 

 profound conceptions of the human spirit more directly 

 called forth than in the study of the heavens and the host 

 thereof." What has been achieved, in fact, does in reality 

 supply us with more leverage — is in effect an accession of 

 strength, an acceleration of our forward movement, the 

 momentum of which will enable us all the more readily to 

 penetrate through opposing forces, gather in with facility 

 the harvests from ever-widening fields, raise more and 

 more imposing and intellectual temples ; and the darkness 

 which now envelops many problems will be overpowered 

 by the concentration of light from many scattered sources. 

 Dr. Huggins, speaking of fifty years ago, says: " At the 

 time any knowledge of the chemical nature and of the 

 physics of the heavenly bodies was regarded as not 

 only impossible of attainment by any methods of direct 

 observation, but as, indeed, lying altogether outside the 

 limitations imposed upon man by his senses, and by the 

 fixity of his position upon the earth. It could never be, it 

 was confidently thought, more than a matter of presump- 

 tion whether even the matter of the sun, and much less 

 that of the stars, was of the same nature as that of the 

 earth, and the unceasing energy radiated from it due to 

 such matter at a high temperature." Yet these impos- 

 sibles have long since been subordinated to laboratory 

 routine ; the prism — more potent than " Agrippa's magic 



lens — unlocked the door behind which had lain the un- 

 known mystery of the heavenly bodies. 



The microscope as an optical instrument has advanced 

 incomparably during the last twenty years. As Dr. 

 Dallinger states, this has been dependent upon advances of 

 I a structural character, leading to a close approximation to 

 perfect corrections in its spherical and chromatic aberra- 

 tions as an optical apparatus, and in the adoption of a 

 theory explaining the principles of vision. Still this, 

 although it has carried us immensely beyond the practical 

 limits of a quarter of a century ago, is also limited in its 

 application. The great "apertures" of modern objectives 

 involved the discovery of new optical glass, and the per- 

 fected optical system (the "apochromatic" system) required 

 for its highest results a fluid " medium ' rendering the 

 source of illumination (the condenser), the object itself, 

 and the object-glass homogeneous. The limit of the 

 usefulness of the system is at present the difficulty of 

 finding suitable fluid media, i.t., with suitable refractive 

 and dispersive indices, and at the same time non-injurious 

 to animal and vegetable substances under examination. 

 Thus, the optician has provided an objective having a 

 so-called " numerical aperture" of 1-63, but no medium 

 has yet been found to make it of practical use to the bio- 

 logist. Another way, therefore, has been suggested as 

 practicable, which is such a construction of the optical 

 system as will admit of the most efiicient u;e of smaller 

 wave-lengths only of the light ray ; object-glasses not 

 merely used with monochromatic (blue) light, but so con- 

 structed as to employ it with the finest results with rays 

 having a sufficiently short wave-length to be visually 

 perfect as well as actinically active — the objective being 

 corrected specially for this. It is calculated that with a ray 

 having a wave-length of 0'35 a, instead of ordinary day- 

 light composed of rays of a mean wave-length of 0-55 a, 

 the same advantage would be gained as if apertures of our 

 present objectives were increased from 1'40 to 2-20. When 

 we see what advances have actually been made during the 

 last sixty years, can we not anticipate as much more 

 during the next sixty ? Upon this question a few words 

 from the same specialist wiU greatly assist us. He says : 



" This is the more conceivable on account of the enlarged 

 possibilities that photography — which during the last two 

 decades has been so great an aid to microscopical investi- 

 gation — may yet be enabled to afford. 



" So far, however, as we are able to see, the practical use 

 of the instrument will be brought out — though with more 

 efficiency — along the same lines in which it has been 

 hitherto used : in minute embryology, in the study of the 

 development of cells and the minute structure of organic 

 tissues, animal and vegetable, in morbid anatomy and 

 pathological research, as well as in many departments of 

 physiology — especially in the complete study of minute 

 organic forms directly causing disease to animals and man. 

 This last is a region of great possibility : already remark- 

 able work has been done from which the human race and 

 immense numbers of domestic animals have derived untold 

 benefit. As a department of sanitary science it is, how- 

 ever, in its early days. Advances in the optical power of 

 the microscope and increasing application on the part 

 of qualified and equipped observers, will open an entire 

 world of microscopic work and successful investigation to 

 them. 



" With this also goes the devising by experiment of 

 means of immunity from the scourges arising from these 

 minute organic forms. 



" So, also, the study of minute biology in all its forms, as 

 well as the minute structure of inorganic substances. 

 This is sufiiciently manifest in the work recently done on 



