In this case, though the principal object of the passion, viz, the life or death of his friend, be to him equally uncertain when present as when absent; yet there are a thousand little circumstances of his friend's situation and condition, the knowledge of which fixes the idea, and prevents that fluctuation and uncertainty so near allyed to fear.
Uncertainty is, indeed, in one respect as near allyed to hope as to fear, since it makes an essential part in the composition of the former passion; but the reason, why it inclines not to that side, is, that uncertainty alone is uneasy, and has a reladon of impressions to the uneasy passions.
It is thus our uncertainty concerning any minute circumstance relating to a person encreases our apprehensions of his death or misfortune.
Horace has remarked this phaenomenon.
UT ASSIDENS IMPLUMI BUS PULLUS AVIS SERPENTIUM ALLAPSUS TIRNET, MAGIS RELICTIS; NON, UT ADSIT, AUXILI LATURA PLUS PRESENTIBUS.
[As a bird, watching over her fledgelings, is more afraid of their being attacked by snakes if she were to leave them even though, were she to stay, she would not be any more capable of helping them, when they were with her.] But this principle of the connexion of fear with uncertainty I carry farther, and observe that any doubt produces that passion, even though it presents nothing to us on any side but what is good and desireable.

A virgin, on her bridalnight goes to bed full of fears and apprehensions, though she expects nothing but pleasure of the highest kind, and what she has long wished for.

The newness and greatness of the event, the confusion of wishes and joys so embarrass the mind, that it knows not on what passion to fix itself; from whence arises a fluttering or unsettledness of the spirits which being, in some degree, uneasy, very naturally degenerates into fear.
Thus we still find, that whatever causes any fluctuation or mixture of passions, with any degree of uneasiness, always produces fear, or at least a passion so like it, that they are scarcely to be distinguished.
I have here confined myself to the examination of hope and fear in their most simple and natural situation, without considering all the variations they may receive from the mixture of different views and reflections.

Terror, consternation, astonishment, anxiety, and other passions of that kind, are nothing but different species and degrees of fear.

It is easy to imagine how a different situation of the object, or a different turn of thought, may change even the sensation of a passion; and this may in general account for all the particular sub-divisions of the other affections, as well as of fear.