Why Does a Chanukiya Look Like That?

Rava said: One must kindle another light in addition to the Hanukkah lights in order to use its light, as it is prohibited to use the light of the Hanukkah lights.

... We add a new candle on each and every night, until on the eighth night eight candles are lit...

... Beit Shammai say: On the first day one kindles eight lights and, from there on, gradually decreases the number of lights until, on the last day of Hanukkah, he kindles one light. And Beit Hillel say: On the first day one kindles one light, and from there on, gradually increases the number of lights until, on the last day, he kindles eight lights.

(4)Rem"a: Therefore one should be careful to place the lights in a straight row and not in a circle, since that is like a bonfire. (Hagahot Maimoniot quoting Sefer Mitzvot Katan) It is permitted to kindle with candlesticks, since each light is separated greatly from the other. (Terumat Hadeshen Section 105) One must be careful when preparing lights, even of wax, not to stick them together and kindle them, since that is like a bonfire. (Piskei Mahar"i 65) Even with the lights of the Sabbath and Holy Days one must be careful not to do so. (Or Zarua)

(1) Paragraph 1 — All oils and wicks are fit for use for the Hanukkah light, even if the oils are not drawn after the wick, and the illumination is not held well by those wicks. Rema: However, olive oil is a choice mitzvah, (Mordechai, Kol Bo and Mahari"l) and if olive oil is not available it is a mitzvah with oils whose illumination is pure and clean, and we have the custom in these countries to kindle with wax candles since their illumination is clear like oil.