Kinján reijá

The Gemara asks: But let the tanna teach a case where each one merely claims: I found it, and I would know that the intention of each litigant is to claim: All of it is mine. The Gemara answers: If the tanna would teach only that each one claimed: I found it, I would say that what is the meaning of the claim: I found it? It means: I saw it. In other words, he is claiming that he saw the item first, and he believes that even though it did not reach his possession, he acquired it through mere sight. Since it would have been possible to think that this is an effective claim, the tanna teaches that the litigant states definitively: All of it is mine, to teach that one does not acquire a lost item through sight alone.

[H]e does not acquire [it] through sight. The Mishna teaches us that by merely seeing a lost object, one does not acquire it.
There seems to be a contradiction to this ruling from a Gemara later on 118a. The Gemara there quotes a Mishna in Shekalim which cites a dispute about whether those who guard the growing barley in the Shemittah year must be paid for their labor or not. The first Tanna holds that they must be paid. Otherwise, the barley they are guarding would belong to them and the barley for the Omer offering must belong to the public, not to an individual. R’ Yose holds that the guards can work for free if they so desire.
The Gemara explains that the first Tanna holds that “guarding” the ownerless barley is a way of acquiring it. If the guards are not paid from public funds, they become the legal owners and the Omer offering must be owned by the public. R’ Yose holds that “guarding” the ownerless barley is not an acceptable method of acquiring it. Thus, even if the guards are not paid, the barley does not become their property and may be used for the Omer offering. The Gemara continues to suggest other ways of explaining the dispute, but they all focus around whether “guarding” the growing barley is an acceptable method of acquisition.
The Gemara uses the expression הבטה which literally means looking or watching. Tosfos understands that this is the same as ראיה - seeing, of our Gemara. Thus, we have what appears to be a contradiction. That which [the Gemara] says in Perek Habayis Vehaliyah (below 118a): “watching” an ownerless item is an effective act of acquisition, that is when he did some minimal action, such as constructing a small fence around the barley. Even though he did nothing at all to the barley, “watching” or “guarding” it is an effective act of acquisition, but by merely seeing a lost object and taking no action whatsoever, one does not acquire the object.

Rabba says: The issue of whether, in the case of ownerless property, viewing effects acquisition of it is a dispute between tanna’im. As we learned in a mishna (Shekalim 9b): The watchmen of the sefiḥim, grain that grew without being purposely planted, of the Sabbatical Year ensured that people did not take this ownerless grain, so that it remained available to be used for the omer offering and the two loaves, i.e., the public offering on Shavuot of two loaves from the new wheat. These watchmen take their wages from the collection of the Temple treasury chamber, as they are employed by the Temple treasury. Rabbi Yosei says: One who so desires can volunteer his services and safeguard the grain, and he has the status of an unpaid bailee. The Rabbis said to him: Do you say so? But according to your view, the omer and the two loaves do not come from communal funds as required, since in reality they come from a private individual, i.e., the bailee.