Prentice, J.

The plaintiff assumed the burden of establishing by a preponderance of evidence the defendant’s negligence and her intestate’s freedom from contributory negligence. If she failed to present, in support of each of these two propositions, substantial evidence which should be weighed and considered by the jury, and upon which it reasonably might have reached affirmative conclusions, the nonsuit was properly granted. Booth v. Hart, 43 Conn. 480, 484; Foskett & Bishop v. Swayne, 70 Conn. 74, 75, 76, 38 Atl. 893. The evidence presented must have been such as to furnish a more substantial basis for a conclusion than a mere guess, surmise, or conjecture. Mesite v. Connecticut Co., 82 Conn. 403, 405, 74 Atl. 684; Fay v. Hartford & Springfield Street Ry. Co., 81 Conn. 330, 335, 71 Atl. 364. The plaintiff was bound to remove the issues from the realm of speculation, and to establish facts affording a logical basis for the inferences which she claimed. Morse v. Consolidated Ry. Co., 81 Conn. 395, 399, 71 Atl. 553.

It may be assumed, in accordance with the plaintiff’s contention,^ that evidence was presented from which the *404 jury reasonably might have found the defendant negligent in the premises. It is clear that it could not have been so found that the plaintiff’s intestate was free from contributory negligence. Plaintiff’s counsel make no claim to the contrary. They rest their contention that a prima facie case was made out entirely upon an appeal to the doctrine of supervening negligence as recognized and defined in Smith v. Connecticut Ry. & Ltg. Co., 80 Cohn. 268, 270, 67 Atl. 888; Carroll v. Connecticut Co., 82 Conn. 513, 515, 74 Atl. 897; and Elliott v. New York, N. H. & H. R. Co., 83 Conn. 320, 323, 76 Atl. 298.

A successful appeal to this doctrine imposes upon the plaintiff the duty of showing that the defendant’s servant, the motorman, failed to exercise reasonable care and prudence to save the intestate from harm after the peril of the latter became, or in the exercise of due care ought to have become, known to the former, when by the exercise of such care on the part of the former the intestate would not have been injured. Elliott v. New York, N. H. & H. R. Co., 83 Conn. 320, 76 Atl. 298. A prima facie case, which rested upon this contention, could not be made out until evidence pertinent to this line of inquiry was adduced which furnished some basis for a conclusion more substantial than a guess or surmise. The conduct of the parties is to be considered, and its character as related to prudence determined, in view of the situation presented and with which the actors Were respectively confronted. Until there was something substantial before the jury to enable its members to discover what these circumstances were, they would be left with nothing to afford them a reasonable guide in the inquiry they were called upon to make. This was the situation in which the plaintiff’s evidence left her case as touching any claim of supervening negligence on the part of the defendant. What the circumstances demanded of the motorman for the intestate’s *405 protection depended upon the latter’s position and movements at and after the time he signaled the car, then three hundred feet or more away. Upon this vital point the evidence was wholly uninforming, beyond the fact that he was in the street when he gave his signal. There were eighteen feet of roadway between the curb and the easterly or nearest rail. Where, in this width of street, and how near to the rail, he was at this time, the only witness to the occurrence which the plaintiff produced said that he did not know, and, as to the intestate’s subsequent conduct or movements as the car approached, there was not a word of testimony, direct or circumstantial, beyond the fact that somehow and at some time he came into a position in close enough proximity to the rail to be struck. It may have been, for aught that appears, that he was not in a position of danger until the moment before he was hit. It may have been that the final act of negligence which was the proximate cause of the accident was that of the intestate in moving forward into a position of danger when the car was already upon him, and when the motorman was helpless to avert the result. Elliott v. New York, N. H. & H. R. Co., 83 Conn. 320, 325, 76 Atl. 298. It is possible to build up speculative theories, but they can rest upon no substantial foundation furnished by the evidence.

It may be suggested that the failure of the motorman to turn off the searchlight when he saw, or ought to have seen, the intestate in the street intending to board the car, imports a factor into the situation which materially changes it. Of this claim it is to be noted, in the first place, that it carries the case entirely outside of the complaint, which charges no negligence arising from the use or operation of this light. Moreover, it is apparent, in view of the uncertainty in which the plaintiff left the situation as to the intestate’s position and movements, that this claim can have no substantial basis, *406 unless it be held that the failure, under all circumstances, to turn off such a light when a person ahead exhibits his intention to become a passenger, is negligent conduct in itself. For such a sweeping claim the evidence which the plaintiff produced, including that of her experts, furnished no substantial basis. In fact, the only expert to whom her counsel ventured to ask a question relating to this particular matter, discountenanced any such practice in the case of persons preparing to board a car in the ordinary way.

There is no error.

In this opinion the other judges concurred.